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III.—Notes on Continental Geology and Palæontology

Published online by Cambridge University Press:  01 May 2009

Thomas Davidson
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Extract

During my recent stay at Geneva the eminent geologists MM. F.J. Pictet and P. de Loriol showed me a very considerable number of fossils, which they had collected from the middle and lower portions of the Cretaceous system of Switzerland and Savoy, and carefully explained the position of the beds from which they had been obtained. M. Pictet subsequently, at my request, recorded in manuscript his most recent views in connection with this important topic, of which I will shortly reproduce a translation for the benefit of the readers of the Geological Magazine. He has, however, restricted his table and explanations to the middle and lower portions of the Cretaceous system, because the regions which surround Geneva do not exhibit any representatives or evidence in connection with the upper stages. M. Pictet has also explained his views with reference to the rock which, at the Porte-de-France, contains the Terebratula janitor, and of the Carpathian or Stramberg limestone, which has been placed by M. Hébert at the base of the Cretaceous system, but which others have referred to the Jurassic epoch. The correct determination of the true age of these rocks is a subject of very great importance, since they contain a rich assemblage of species bearing a particular and well-marked stamp, as may be seen by a glance at Professor Suess's admirable monograph, “Die Brachiopoden der Stramberger Schichten,” as well as at those by Zettel, etc., on other classes.

Type
Original Articles
Information
Geological Magazine , Volume 6 , Issue 60 , June 1869 , pp. 251 - 263
Copyright
Copyright © Cambridge University Press 1869

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References

page 251 note 1 See in this connection the Canadian Journal, for 1858, p. 203;Google Scholar Quart. Jour. Geol. Society for 1859, p. 494;Google Scholar Amer. Jour. Science [2] xxxvii., 255, xxxviii. 182;Google Scholar also Geology of Canada, 1863, pp. 643, 669,Google Scholar and Rep. Geol. Canada, 1866, p.230.Google Scholar

page 258 note 1 Mr. Judd informs me that he has at present in preparation descriptions accompanied by illustrations of the species which occur in the beds of the Speeton Clay, so that M. Pictet's earnest request will shortly be complied with.

page 259 note 1 Mr. J. F. Walker favours me with the following remarks: “You have called the Cambridge phosphate bed, Upper Gault, although the people here call it Upper Green Sand. I have long doubted the determination. I think that it has been formed by the denudation of the Gault. 1st. Because the common fossils are Gault species. 2nd. The species characteristic of Warminster are nearly absent. 3rd. The fossils are often waterworn; you seldom find associated bones of reptiles, sometimes the reptile bones are broken and oysters are deposited on the fractured surfaces. 4th. The fossils are nearly always covered with the phosphate deposit, oysters are attached to the nodules; the nodules are rolled, appear to have been brittle, as I have found pieces broken, and the characteristic Plicatula attached to the broken surface, which would tend to prove that they had not been formed where they are found. 5th. The bed is thin, full of nodules, bones and shells; the green grains pass up into the Chalk, above the nodule bed, the clay below contains very few fossils (I have obtained fish vertebræ and Plicatula pectinoides). Now if the sea coast had consisted of Gault Clay, which was destroyed by the sea, the nodules, bones, shells, might be washed out (as the denudation of the drift clay forms beds of gravel) and form the Cambridge bed. This would give the reason for the mass of nodules, etc., accumulated in so small a space; some of the bones need not have rolled for a long time, but might be carried by currents into deep water, then we might get associated bones. 6th. It is possible that T. gracilis and some others may be of the age of the deposit, and may be found at the base of the Chalk. Bones that have not been through the washing mills are often waterworn, the mills used to be blamed for the appearance of the fossils.

page 260 note 1 Mr. Judd is happy to be able to bear his testimony to the relations of the beds which M. Von Strombeck has made with so much skill and labour. When in Germany he saw most of the beds which he refers to in his table, many of them under his own guidance; but as there is no good general section in Brunswick, and detached stone pits, brick yards, etc., form the only means of study, he believes that considerable changes may still have to be made in the grouping of the beds.