268 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



An examination of the fossil contents of the gypsum-series with 

 those of the underlying nummulitic rocks does not show one form ex- 

 tending through both formations. As the lithological character also 

 of these two formations is so totally dissimilar, I have thought it best 

 to describe them separately. Still, however, when the universal and 

 perfect conformability of the gypsiferous marls to the nummulitic 

 limestone is considered (whether the beds of the latter lie horizontally, 

 or rise in lofty domes), we cannot by any means pronounce them to 

 belong to a different geological epoch, but rather consider them as a 

 transition from the older to the newer tertiary period. 



I am disposed to think that a sudden elevation of the whole bottom 

 of the ocean took place at the close of the period when the num- 

 mulitic limestone was deposited, by which the species then living 

 were totally extinguished. This elevation must have been accom- 

 panied and succeeded by the frequent discharge of sulphuric vapours 

 from below, which, acting upon the calcareous matter held in solu- 

 tion by the water, deposited it in the form of sulphate of lime. I 

 am the more inclined to adopt this mode of accounting for the origin 

 of this mineral deposit, because it occupies no fixed position in the 

 marls, but is stratified and intercalated irregularly among them, gene- 

 rally however in their lowest part. Where gypsum occurs, it usually 

 spreads over a large surface, showing it to be the result of a widely 

 extended cause. The entire absence of animal life during its deposi- 

 tion has frequently been remarked. 



The order of superposition of the beds of this formation, as above 

 described, differs materially from that observed by Mr. W. J. Hamilton 

 of the beds of the same formation in Asia Minor generally. Tbat 

 gentleman noticed the variegated marls and gypsum resting uncon- 

 formably * upon underlying sandstones, which latter were in juxta- 

 position to the nummulitic limestone. 



On the flanks of the Zagros, however, as I have endeavoured to 

 show, the marls and gypsums are the lower beds, and rest conform- 

 ably on the limestone, while the sandstones are superimposed upon 

 them. 



I do not think that this inversion of order need be of serious im- 

 portance, when the great distance between the deposits (750 geogra- 

 phical miles) is taken into consideration. It is evident, from the very 

 numerous layers in the various beds, that continual changes occurred ; 

 and therefore there need be no difficulty in supposing that, while 

 sandstones were undergoing deposition in Asia Minor, marls and 

 gypsums might be forming along the Zagros, and vice versa. 



The marls and gypsum of Mr. Hamilton's sections (Quart. Journ. 

 Geol. Soc. vol. V. p. 373) are represented as lying horizontally upon 

 the elevated and even vertical sandstones. This, however, may be 

 the result of the Taurus having been thrown up at a different period 

 from the Zagros. It is by no means improbable that in some other 



* Quart. Journ. Geol. Soc. vol. v. p. 373. In another district, however, of 

 Asia Minor, Mr. Hamilton observed gypsiferous beds conformable with the red 

 and yellow marl and sandstone ; see Trans. Geol. Soc. Lond. 2 ser. vol. v. pp. 590 

 & 592.— Ed. 



