T. Davidson — Continental Geology. 251 



silicates of peculiar types. Some of these are in great part magnesian, 

 others consist of compounds like anorthite and labradorite, highly 

 aluminous basic silicates, in which lime and soda enter to the almost 

 complete exclusion of magnesia and other bases ; while in the 

 masses of pinite or agalmatolite rock, we have a similar aluminous 

 silicate, in which lime and magnesia are wanting, and potash is the 

 predominent alkali. In such sediments as these just enumerated, 

 we find the representatives of eruptive rocks like peridotite, phono- 

 lite, leucitophyre, and similar rocks which are so many exceptions in 

 the basic group of Bunsen. As, however, they are represented 

 in the sediments of the earth's crust, their appearance as exotic 

 rocks, consequent upon a softening and extravasation of the more 

 easily liquefiable strata of deeply buried formations, is readily and 

 simply explained.^ 



The object of the present communication has been to call the 

 attention of geologists to the neglected views of Keferstein and 

 Herschel, which I have endeavoured to extend and to adapt to the 

 present state of our knowledge. It is proposed in another paper to 

 consider the question of the agencies which have regulated the geo- 

 graphical distribution of volcanic phenomena both in ancient and in 

 modern times. 



Montreal, Canada, March, 1869. 



III. — Notes on Continental Geology and Paleontology. 



By Thomas Davidson, F.R.S., F.G.S. 



[Continued from p . 205). 



(Part III.) 



DUEING 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 im- 

 portant 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 Terehratula janitor, and of the Carpathian or Stramberg 

 limestone, which has been placed by M. Hebert 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 assem- 



' See in this connection the Canadian Journal, for 1858, p. 203; Quart. Jour. 

 Geol. Society for 1859, p. 494 ; Amer. Jour. Science [2] xxxvii., 255, xxxviii. 182 ; 

 also Geology of Canada, 1863, pp. 643, 669, and Eep. Geol. Canada, 1866, p. 230. 



