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Some comments on Van Hilten's discussion on ancient continental configurations
531
SOME COMMENTS ON VAN HILTEN’S CONTINENTAL CONFIGURATIONS
DISCUSSION ON ANCIENT
K.M. CREER Department of Physics, (Great Britain) (Received
University of Newcastle upon Tyne, Newcastle upon Tyne
March 3, 1965)
INTRODUCTION
Van Hilten’s (1965) two main criticisms of my deductions from palaeomagnetic data concerning the distribution of the continents in the Upper Palaeozoic (Creer, 1964a, b) are: (1) That reconstructions of the continents such as.Du Toit’s deduced from geological evidence are hypothetical and that there is no point in testing palaeomagnetic data against them. (2) That the revised Devonian pole for Europe (Chamalaun, 1963, 1964; Chamalaun and Creer, 1963, 1964) is based on results from incompletely cleaned samples. The first indicates an inadequate appreciation of the contribution made by geologists towards the now widespread acceptance of the hypothesis of drift. The second criticism is based on a misunderstanding of geometry and is therefore invalid. In the following, these and other points he raises are answered at greater length.
PALAEOMAGNETIC
VERSUS GEOLOGICAL
EVIDENCE
Do palaeomagnetic data constitute the only reliable evidence for drift? Should is the geological evidence be disregarded ? The value of palaeomagnetism surely that it has provided quantitative evidence for drift. Before the advent of palaeomagnetism the geological evidence for drift (the fit of coastlines, etc.) had been considered by some geologists to be due to chance. The independent evidence from palaeomagnetism has now convinced most geologists that these fears were unfounded. A large volume of palaeomagnetic work done during the past decade has established the principle that the continents have drifted relative to one another in the geological past. Palaeomagnetic data for South America and Africa (Creer, 1964a, c, 1965a) lead quite clearly to a reconstruction indistinguishable from that obtained by mating coastlines. Therefore this latter criterion must now be accepted as meaningful. Reconstructions based upon it are no longer hypothetical, thanks to palaeomagnetism. The fit of coastlines, especially across the North and South Atlantic Oceans, is so good (Bullard et al., 1965) that I doubt whether the time will ever come ‘l’ectonophysics,
1 (6) (1965) 531-535
call reassemble the continents as parts ol’ Laurasia and Gondw;tnalantl with equal precision using palaeomagnetic data alone. The palaeomagnetic method WI) nevertheless be used to make an iii
when we
valuable contribution to our knowledge of the development of the earth. Its quantitative character enables us to investigate polar wandering across the reconstructed supercontinents. It is ;I much more reliable guide to ancietil latitudes than palaeoclimatic studies which are essentially qualitative. It can tell us when the supercontinents of Laurasia and Gondwanaland started to break up and how the continents as we know them today subsequently drifted apart. It will probably tell us how long these supercontinents existed and whether they are formed as a result of an earlier episode of continental drift or whether their origin was primeval (Creer, 1965b). In these applications there is 110doubt that the palaeomagnetic method is as good as any yet developed. It should, however, be remembered that it is not free of hypothesis: it is usually supposed that the palaeogeomagnetic field was always axial and dipolar. This hypothesis, although a fruitful one, has not been proved beyond doubt. Therefore palaeomagnetic data should not be considered in isolation as suggested by Van Hilten. Conclusions drawn from them should be compared with those derived from other branches of geology and geophysics al every available opportunity. It is by free interplay between the various disciplines that science advances.
THE REVISED
DEVONIAN
POLE FOR EUROPE
The conclusion that we should adopt a revised Devonian pole for Europe was not arrived at lightly. The original one (Creer, 1955, 1957) was subsequently apparently confirmed by palaeomagnetic work in Europe, Asia and North America. It was only with great reluctance that Chamalaun and I (Chamalaun and Creer, 1963, 1964; Chamalaun 1964) were led to suggest that a widespread and severe remagnetization of Palaeozoic rocks must have taken place in the Laurasian continents during the Permo-Carboniferous. Various possible explanations of the rather complex picture we are building up from the natural magnetization of Devonian rocks were considered at the NATO Palaeoclimates Conference in January 1963 (Creer, 1964c). Whether our conclusions are correct will only be decided by patient research work involving careful demagnetization experiments on Lower Palaeozoic formations we suspect have been remagnetized. It is not a question of magnetic instability. 111Van Hilten’s re-interpretation of our thermal experiments in the Old Red Sandstone rocks, he notes that the great circles of demagnetization converge towards an area near the point N 35”E with almost zero inclination. This he suggests is the true primary direction of magnetization. The reader should note that the great circles (Van Hilten, 1965, fig.3E) diverge from a “point” S 35% and approximately horizontal. This is the mean “virgin” direction of magnetization of the specimens under consideration. Now it is an elementary fact that a great circle passes through both ends of any veLtor lying in the plane it represents. Van Hilten does not appear to realise this! The great circles in fig.3E thus diverge from the mean direction of virgin magnetization, pass through the weak primary direction (which we have adopted as the true Devonian field) and converge on a purely fictitious Tectonophysics,
1 (6) (1965) 531-5X
ANCIENT
CONTINENTAL
CONFIGURATIONS:
A DISCUSSION
533
point, 180’ from the mean “virgin” direction. This point which Van Hilten has taken to be the primary direction of magnetization is thus meaningless. His extrapolation of our demagnetization great circles is quite unjustified. Since the magnetization after cleaning was so weak compared with the virgin magnetization we naturally found that the directions obtained from individual specimens were not very tightly grouped. The pole calculated from them however was not significantly different from that obtained by Stubbs (1958) who made a comprehensive survey of the Devonian lavas of the Midland Valley of Scotland. We therefore decided to use Stubbs’ result as our suggested revised Devonian pole. I am, of course, aware of Nairn’s (1960) result for the Midland Valley Lavas quoted by Van Hilten, as the work was done in this laboratory. Stubbs’ survey was, however, much more comprehensive than Nairn’s, and some of his samples, like Nairn’s, agreed with my original Devoniah work on the Old Red Sandstones (Creer, 1955, 1957). However, the fact remains that the Old Red Sandstones having been subjected to a stringent thermal analysis reveal a weak component of magnetization in agreement with Stubbs’ principle direction. We have concluded from the results of these experiments that the virgin direction of magnetization of the Old Red Sandstones, with which Nairn’s result and also the Russian Devonian data agree, was imposed later in the Permo-Carboniferous. Nairn’s rocks were not subjected to such thermal analysis. Neither were the Russian rocks. MAGNETIC
AND STRATIGRAPHIC
AGES
These are not necessarily the same for sedimentary rocks. The secondary magnetization imposed on the Old Red Sandstones in the Permo-Carboniferous is extremely stable. Its intensity decreases by only 5% when subjected to a.c. demagnetizing fields of 2,000 Oe (Oersteds). The Russian Devonian data quoted by Van Hilten (Vlasov and Kovalenko, 1963) are derived from rocks which have been found stable in a.c. fields of only 500 Oe. The only other stability test carried out was d.c. demagnetization. A d.c. field of 60 Oe. was required to demagnetize them. But this sort of test is valueless in deducing the stability or age of the natural remanence for one merely magnetizes initially unmagnetized soft material to the same intensity as that of the natural remanence of the hard material in the rock but in the opposite direction. The thermal treatment the Russian workers carried out comprised demagnetization of a remanent magnetization produced in the samples in the laboratory by a strong field of 5,000 Oe. The natural remanent magnetization, however, was not subjected to thermal demagnetization. So the possibility that these rocks contain a high temperature component as found by Chamalaun in the Old Red Sandstones has not been investigated. All the Russian workers did was to remove a viscous component of magnetization by treatment in an a.c. field of 150 Oe. There is no proof whatever that these rocks did not receive their magnetization in the Permo-Carboniferous. The presence of normal and reversed zones does not rule out this possibility, for they could have been impressed in the rocks by crystallization magnetization long after deposition. Van Hilten also criticises the fact that on my reconstruction the ‘Tectonophysics, 1 (6) (1965) 531-535
Australian Devonian and Silurian poles do not coincide with the African, South American and revised European Devonian and Silurian poles. What proof is there that the magnetization of all these rocks is of the same age? None. In my paper (Creer, 1964a) this is clearly pointed out. The fact that all these poles lie on the common curve may, however, be significant. Could it be that we have a new method of magnetic age correlation between continents depending on the wandering of the pole across Gondwanaland in the Upper Palaeozoic? This is a fruitful field for research.
SELECTION
OF DATA
Probably the most comprehensive list of palaeomagnetic data yet assembled was presented by Irving (1964). Neither ln this list, nor in any other similar list is it intended that the reader should assess the full signtficance of data included without reference to the original papers. Information about numbers of specimens, whether any attempts at cleaning have been made, etc.., are given but the information which can be presented in table form is strictly limited. It has never been claimed by the compilers of these lists that all the data presented are reliable. The purpose rather has been to collect together in a convenient form all available data and to give source references. In attempting a synthesis of world wide data one can only expect to run into trouble, as Van Hilten and others have done, by indiscriminate use of data listed in these tables. It is not sufficient to select data merely by reference to statistical information quoted. A small circle of confidence does not necessarily indicate reliability. It tells us nothing of systematic errors such as are produced by severe remagnetization. In analysing data, the only sensible procedure is to derive some criteria of selecting reliable from doubtful data from one’s own first hand experiences in the subject. In my analysis, the reason why certain data were selected are clearly stated (Creer, 1964a), and the data used are listed, so that my choice of data can be subjected to experimental test by others. My main criterion resulted from the experiments on the Old Red Sandstones from which the revised Devonian pole for Britain was derived. In my reconstruction of the continents and also in Du Toit’s, most of Laurasia occupied low latitudes in the Pennsylvanian and Permian. Red beds were formed in all the Laurasian continents at some time during this interval. Conditions must then have been ideal for the deposition of red cement in Lower Palaeozoic rocks and hence for secondary magnetization to take place over a very wide area. A similar process is occurring today in tropical regions. I have found evidence in northeastern Brazil of widespread remagnetization of rocks down to a considerable depth by the Tertiary or Quaternary geomagnetic fields. While Laurasia was at low latitudes, Gondwanaland was in polar latitudes. Hence Palaeozoic rocks in Gondwanaland were not remagnetized during the Permo-Carboniferous. Van Hilten criticises my choice of North American data and my rejec-
tion of the Russian Devonian data. Experiments such as Chamalaun and I described have not yet been done on North American or Russian rocks. Hence the magnetic ages of some Russian and North American Lower Palaeozoic sediments are questionable because of their similar lithology to the Old Red
Tectonophysics, 1 (f.i)(1965) X31-535
ANCIENT CONTINENTAL
CONFIGURATIONS:
A DISCUSSION
535
Sandstones. Certain data from North American rocks (not red beds) were noted to fit with the revised European Devonian pole and with the geological evidence. Whether or not I was justified in using these data in preference to the others included in palaeomagnetic lists will be decided only as a result of experiment and not by discussion. But let me stress this. Adoption of these North American data did not form the main basis of my reconstruction. It did, however, enable me to complete a palaeomagnetic history consistent both in itself and with geological evidence. REFERENCES Bullard, E., Everitl, J.E. and Smith, A.G., 1965. The fit of the continents around the Atlantic. Phil. Trans. Roy. Sot. London, Ser. A, in press. Chamalaun, F.H., 1963. Thermal Demagnetization of Red Sediments. Thesis, University of Durham, 227 pp. Chamalaun, F.H., 1964. Origin of the secondary magnetization of the Old Red Sandstones from the Anglo-Welsh cuvette. J. Geophys. Res., 69 (20): 43274336. Chamalaun, F.H. and Creer, K.M., 1963. A revised Devonian pole for Britain. Nature, 198: 375. Chamalaun, F.H. and Creer, K.M., 1964. Thermal demagnetization studies on the Old Red Sandstones of the Anglo-Welsh cuvette. J. Geophys. Res., 69 (8): 1607-1616. Creer, K.M., 1955. A Palaeomagnetic Survey of certain Rocks from Britain. Thesis, University of Cambridge, 203 pp. Creer, K.M., 1957. The natural remanent magnetization of certain stable rocks from Great Britain. Phil. Trans. Roy. Sot. London, Ser. A, 250: 111. Creer, K.M., 1964a. A reconstruction of the continents for the Upper Palaeozoic from palaeomagnetic data. Nature, 203:(4950): 1115-1120. Creer, K.M., 1964b. Palaeomagnetic data and Du Toit’s reconstruction of Gondwanaland. Nature, 204 (4956): 36S-370. Creer, K.M., 1964c. Palaeolatitudes of the continents in the Devonian as revealed by the natural remanent magnetization of rocks. In: A.E.M. Nairn (Editor), Problems of Palaeoclimatology. Interscience, London, pp.269-284. Creer, K.M., 1965a. Palaeomagnetic data from Gondwanic continents. Phil. Trans. Roy. Sot, London, Ser. A, in press. Creer, K.M., 1965b. An expanding earth? Nature, 205: 534544. Irving, E., 1964. Palaeomagnetism and its Application to Geological and Geophysical Problems. Wiley, New York, N.Y., 399 pp. Nairn, A.E.M., 1960. Paleomagnetic results from Europe. J. Geol., 68 (3): 285306. Stubbs, P.H.S., 1958. Continental Drift and Polar Wandering, A Palaeomagnetic Study of British and European Trias and of the British Old Red Sandstones. Thesis, University of London, 158 pp. Van Hilten, D., 1965. Discussion of some recent papers on ancient continental configurations reconstructed from paleomagnetic evidence. Tectonophysics, 1 (6): 521-530. Vlasov, A.Y. and Kovalenko, G.V., 1963. Magnetism of transitional layers between zones with direct and reverse magnetization. Bull. Acad. Sci. U.S.S.R., Geophys. Ser. (English transl.), 1963 (4): 343-347.
Tectonophysics,
1 (6) (1965) 531-535
SOME COMMENTS ON VAN HILTEN’S CONTINENTAL CONFIGURATIONS
DISCUSSION ON ANCIENT
K.M. CREER Department of Physics, (Great Britain) (Received
University of Newcastle upon Tyne, Newcastle upon Tyne
March 3, 1965)
INTRODUCTION
Van Hilten’s (1965) two main criticisms of my deductions from palaeomagnetic data concerning the distribution of the continents in the Upper Palaeozoic (Creer, 1964a, b) are: (1) That reconstructions of the continents such as.Du Toit’s deduced from geological evidence are hypothetical and that there is no point in testing palaeomagnetic data against them. (2) That the revised Devonian pole for Europe (Chamalaun, 1963, 1964; Chamalaun and Creer, 1963, 1964) is based on results from incompletely cleaned samples. The first indicates an inadequate appreciation of the contribution made by geologists towards the now widespread acceptance of the hypothesis of drift. The second criticism is based on a misunderstanding of geometry and is therefore invalid. In the following, these and other points he raises are answered at greater length.
PALAEOMAGNETIC
VERSUS GEOLOGICAL
EVIDENCE
Do palaeomagnetic data constitute the only reliable evidence for drift? Should is the geological evidence be disregarded ? The value of palaeomagnetism surely that it has provided quantitative evidence for drift. Before the advent of palaeomagnetism the geological evidence for drift (the fit of coastlines, etc.) had been considered by some geologists to be due to chance. The independent evidence from palaeomagnetism has now convinced most geologists that these fears were unfounded. A large volume of palaeomagnetic work done during the past decade has established the principle that the continents have drifted relative to one another in the geological past. Palaeomagnetic data for South America and Africa (Creer, 1964a, c, 1965a) lead quite clearly to a reconstruction indistinguishable from that obtained by mating coastlines. Therefore this latter criterion must now be accepted as meaningful. Reconstructions based upon it are no longer hypothetical, thanks to palaeomagnetism. The fit of coastlines, especially across the North and South Atlantic Oceans, is so good (Bullard et al., 1965) that I doubt whether the time will ever come ‘l’ectonophysics,
1 (6) (1965) 531-535
call reassemble the continents as parts ol’ Laurasia and Gondw;tnalantl with equal precision using palaeomagnetic data alone. The palaeomagnetic method WI) nevertheless be used to make an iii
when we
valuable contribution to our knowledge of the development of the earth. Its quantitative character enables us to investigate polar wandering across the reconstructed supercontinents. It is ;I much more reliable guide to ancietil latitudes than palaeoclimatic studies which are essentially qualitative. It can tell us when the supercontinents of Laurasia and Gondwanaland started to break up and how the continents as we know them today subsequently drifted apart. It will probably tell us how long these supercontinents existed and whether they are formed as a result of an earlier episode of continental drift or whether their origin was primeval (Creer, 1965b). In these applications there is 110doubt that the palaeomagnetic method is as good as any yet developed. It should, however, be remembered that it is not free of hypothesis: it is usually supposed that the palaeogeomagnetic field was always axial and dipolar. This hypothesis, although a fruitful one, has not been proved beyond doubt. Therefore palaeomagnetic data should not be considered in isolation as suggested by Van Hilten. Conclusions drawn from them should be compared with those derived from other branches of geology and geophysics al every available opportunity. It is by free interplay between the various disciplines that science advances.
THE REVISED
DEVONIAN
POLE FOR EUROPE
The conclusion that we should adopt a revised Devonian pole for Europe was not arrived at lightly. The original one (Creer, 1955, 1957) was subsequently apparently confirmed by palaeomagnetic work in Europe, Asia and North America. It was only with great reluctance that Chamalaun and I (Chamalaun and Creer, 1963, 1964; Chamalaun 1964) were led to suggest that a widespread and severe remagnetization of Palaeozoic rocks must have taken place in the Laurasian continents during the Permo-Carboniferous. Various possible explanations of the rather complex picture we are building up from the natural magnetization of Devonian rocks were considered at the NATO Palaeoclimates Conference in January 1963 (Creer, 1964c). Whether our conclusions are correct will only be decided by patient research work involving careful demagnetization experiments on Lower Palaeozoic formations we suspect have been remagnetized. It is not a question of magnetic instability. 111Van Hilten’s re-interpretation of our thermal experiments in the Old Red Sandstone rocks, he notes that the great circles of demagnetization converge towards an area near the point N 35”E with almost zero inclination. This he suggests is the true primary direction of magnetization. The reader should note that the great circles (Van Hilten, 1965, fig.3E) diverge from a “point” S 35% and approximately horizontal. This is the mean “virgin” direction of magnetization of the specimens under consideration. Now it is an elementary fact that a great circle passes through both ends of any veLtor lying in the plane it represents. Van Hilten does not appear to realise this! The great circles in fig.3E thus diverge from the mean direction of virgin magnetization, pass through the weak primary direction (which we have adopted as the true Devonian field) and converge on a purely fictitious Tectonophysics,
1 (6) (1965) 531-5X
ANCIENT
CONTINENTAL
CONFIGURATIONS:
A DISCUSSION
533
point, 180’ from the mean “virgin” direction. This point which Van Hilten has taken to be the primary direction of magnetization is thus meaningless. His extrapolation of our demagnetization great circles is quite unjustified. Since the magnetization after cleaning was so weak compared with the virgin magnetization we naturally found that the directions obtained from individual specimens were not very tightly grouped. The pole calculated from them however was not significantly different from that obtained by Stubbs (1958) who made a comprehensive survey of the Devonian lavas of the Midland Valley of Scotland. We therefore decided to use Stubbs’ result as our suggested revised Devonian pole. I am, of course, aware of Nairn’s (1960) result for the Midland Valley Lavas quoted by Van Hilten, as the work was done in this laboratory. Stubbs’ survey was, however, much more comprehensive than Nairn’s, and some of his samples, like Nairn’s, agreed with my original Devoniah work on the Old Red Sandstones (Creer, 1955, 1957). However, the fact remains that the Old Red Sandstones having been subjected to a stringent thermal analysis reveal a weak component of magnetization in agreement with Stubbs’ principle direction. We have concluded from the results of these experiments that the virgin direction of magnetization of the Old Red Sandstones, with which Nairn’s result and also the Russian Devonian data agree, was imposed later in the Permo-Carboniferous. Nairn’s rocks were not subjected to such thermal analysis. Neither were the Russian rocks. MAGNETIC
AND STRATIGRAPHIC
AGES
These are not necessarily the same for sedimentary rocks. The secondary magnetization imposed on the Old Red Sandstones in the Permo-Carboniferous is extremely stable. Its intensity decreases by only 5% when subjected to a.c. demagnetizing fields of 2,000 Oe (Oersteds). The Russian Devonian data quoted by Van Hilten (Vlasov and Kovalenko, 1963) are derived from rocks which have been found stable in a.c. fields of only 500 Oe. The only other stability test carried out was d.c. demagnetization. A d.c. field of 60 Oe. was required to demagnetize them. But this sort of test is valueless in deducing the stability or age of the natural remanence for one merely magnetizes initially unmagnetized soft material to the same intensity as that of the natural remanence of the hard material in the rock but in the opposite direction. The thermal treatment the Russian workers carried out comprised demagnetization of a remanent magnetization produced in the samples in the laboratory by a strong field of 5,000 Oe. The natural remanent magnetization, however, was not subjected to thermal demagnetization. So the possibility that these rocks contain a high temperature component as found by Chamalaun in the Old Red Sandstones has not been investigated. All the Russian workers did was to remove a viscous component of magnetization by treatment in an a.c. field of 150 Oe. There is no proof whatever that these rocks did not receive their magnetization in the Permo-Carboniferous. The presence of normal and reversed zones does not rule out this possibility, for they could have been impressed in the rocks by crystallization magnetization long after deposition. Van Hilten also criticises the fact that on my reconstruction the ‘Tectonophysics, 1 (6) (1965) 531-535
Australian Devonian and Silurian poles do not coincide with the African, South American and revised European Devonian and Silurian poles. What proof is there that the magnetization of all these rocks is of the same age? None. In my paper (Creer, 1964a) this is clearly pointed out. The fact that all these poles lie on the common curve may, however, be significant. Could it be that we have a new method of magnetic age correlation between continents depending on the wandering of the pole across Gondwanaland in the Upper Palaeozoic? This is a fruitful field for research.
SELECTION
OF DATA
Probably the most comprehensive list of palaeomagnetic data yet assembled was presented by Irving (1964). Neither ln this list, nor in any other similar list is it intended that the reader should assess the full signtficance of data included without reference to the original papers. Information about numbers of specimens, whether any attempts at cleaning have been made, etc.., are given but the information which can be presented in table form is strictly limited. It has never been claimed by the compilers of these lists that all the data presented are reliable. The purpose rather has been to collect together in a convenient form all available data and to give source references. In attempting a synthesis of world wide data one can only expect to run into trouble, as Van Hilten and others have done, by indiscriminate use of data listed in these tables. It is not sufficient to select data merely by reference to statistical information quoted. A small circle of confidence does not necessarily indicate reliability. It tells us nothing of systematic errors such as are produced by severe remagnetization. In analysing data, the only sensible procedure is to derive some criteria of selecting reliable from doubtful data from one’s own first hand experiences in the subject. In my analysis, the reason why certain data were selected are clearly stated (Creer, 1964a), and the data used are listed, so that my choice of data can be subjected to experimental test by others. My main criterion resulted from the experiments on the Old Red Sandstones from which the revised Devonian pole for Britain was derived. In my reconstruction of the continents and also in Du Toit’s, most of Laurasia occupied low latitudes in the Pennsylvanian and Permian. Red beds were formed in all the Laurasian continents at some time during this interval. Conditions must then have been ideal for the deposition of red cement in Lower Palaeozoic rocks and hence for secondary magnetization to take place over a very wide area. A similar process is occurring today in tropical regions. I have found evidence in northeastern Brazil of widespread remagnetization of rocks down to a considerable depth by the Tertiary or Quaternary geomagnetic fields. While Laurasia was at low latitudes, Gondwanaland was in polar latitudes. Hence Palaeozoic rocks in Gondwanaland were not remagnetized during the Permo-Carboniferous. Van Hilten criticises my choice of North American data and my rejec-
tion of the Russian Devonian data. Experiments such as Chamalaun and I described have not yet been done on North American or Russian rocks. Hence the magnetic ages of some Russian and North American Lower Palaeozoic sediments are questionable because of their similar lithology to the Old Red
Tectonophysics, 1 (f.i)(1965) X31-535
ANCIENT CONTINENTAL
CONFIGURATIONS:
A DISCUSSION
535
Sandstones. Certain data from North American rocks (not red beds) were noted to fit with the revised European Devonian pole and with the geological evidence. Whether or not I was justified in using these data in preference to the others included in palaeomagnetic lists will be decided only as a result of experiment and not by discussion. But let me stress this. Adoption of these North American data did not form the main basis of my reconstruction. It did, however, enable me to complete a palaeomagnetic history consistent both in itself and with geological evidence. REFERENCES Bullard, E., Everitl, J.E. and Smith, A.G., 1965. The fit of the continents around the Atlantic. Phil. Trans. Roy. Sot. London, Ser. A, in press. Chamalaun, F.H., 1963. Thermal Demagnetization of Red Sediments. Thesis, University of Durham, 227 pp. Chamalaun, F.H., 1964. Origin of the secondary magnetization of the Old Red Sandstones from the Anglo-Welsh cuvette. J. Geophys. Res., 69 (20): 43274336. Chamalaun, F.H. and Creer, K.M., 1963. A revised Devonian pole for Britain. Nature, 198: 375. Chamalaun, F.H. and Creer, K.M., 1964. Thermal demagnetization studies on the Old Red Sandstones of the Anglo-Welsh cuvette. J. Geophys. Res., 69 (8): 1607-1616. Creer, K.M., 1955. A Palaeomagnetic Survey of certain Rocks from Britain. Thesis, University of Cambridge, 203 pp. Creer, K.M., 1957. The natural remanent magnetization of certain stable rocks from Great Britain. Phil. Trans. Roy. Sot. London, Ser. A, 250: 111. Creer, K.M., 1964a. A reconstruction of the continents for the Upper Palaeozoic from palaeomagnetic data. Nature, 203:(4950): 1115-1120. Creer, K.M., 1964b. Palaeomagnetic data and Du Toit’s reconstruction of Gondwanaland. Nature, 204 (4956): 36S-370. Creer, K.M., 1964c. Palaeolatitudes of the continents in the Devonian as revealed by the natural remanent magnetization of rocks. In: A.E.M. Nairn (Editor), Problems of Palaeoclimatology. Interscience, London, pp.269-284. Creer, K.M., 1965a. Palaeomagnetic data from Gondwanic continents. Phil. Trans. Roy. Sot, London, Ser. A, in press. Creer, K.M., 1965b. An expanding earth? Nature, 205: 534544. Irving, E., 1964. Palaeomagnetism and its Application to Geological and Geophysical Problems. Wiley, New York, N.Y., 399 pp. Nairn, A.E.M., 1960. Paleomagnetic results from Europe. J. Geol., 68 (3): 285306. Stubbs, P.H.S., 1958. Continental Drift and Polar Wandering, A Palaeomagnetic Study of British and European Trias and of the British Old Red Sandstones. Thesis, University of London, 158 pp. Van Hilten, D., 1965. Discussion of some recent papers on ancient continental configurations reconstructed from paleomagnetic evidence. Tectonophysics, 1 (6): 521-530. Vlasov, A.Y. and Kovalenko, G.V., 1963. Magnetism of transitional layers between zones with direct and reverse magnetization. Bull. Acad. Sci. U.S.S.R., Geophys. Ser. (English transl.), 1963 (4): 343-347.
Tectonophysics,
1 (6) (1965) 531-535