222 Notices of Memoirs — Prof. J. B. Dana — On Lithology. 



Of the remainder, the absence of Milliolidea (of Spiroculina tenuis one 

 example was found), Amphistegina, Heterostegina, and Polystomella 

 is noticeable, while the quantity of Rhabdoidea (38 species), Cristel- 

 laroidea (14:), Globigerinidea (17), not only in the number of species, 

 but also of individuals, is striking, and a deep sea is indicated, and 

 is confirmed by the Eadiolarian fauna, though the Badiolaria are 

 only found scattered in the clay. Of the Foraminifera 63 are found 

 at Baden, near Vienna ; 38 are known living ; and 52 are supposed 

 to be extinct. The Molluscan fauna is also very similar to that of 

 the Baden beds. 



The tripoli beds, which are below the "tufo," were evidently 

 deposited in a still deeper sea, as shown by the rich Eadiolarian 

 fauna of 109 species, studied by Mr. Stohr. It most nearly resembles 

 the tripoli of Caltanisetta, from which Ehrenberg described 31 

 species ; but the Grotte beds furnish 68 new species, which will 

 shortly be figured and described, and of the rest 29 are known 

 living, about half of these in the Mediterranean. Some families 

 and genera, hitherto unknown in the fossil state, are now described ; 

 for instance, the genus Euchitonia, which was previously only known 

 as recent, furnishes several species, some identical with those found in 

 the sea near Messina. The author says that this genus is sometimes 

 so abundantly represented at Grotte that we might almost call this 

 tripoli a mass of Euchitonia. 



The conclusions arrived at are that both tripoli and "tufo" belong 

 to the Tortonian (Miocene), and were deposited in deep water ; after- 

 wards there was elevation of the land, and lacustrine conditions 

 supervened, when the deposits which now yield the sulphur were 

 formed, during the Messinian I. II. and probably III. (of Mayer), 

 after which sinking of the land and marine conditions followed. 



A. W. W. 



II. — On Some Points in Lithology. By Prof. J. D. Dana. 



UNDER the above title Prof. Dana has recently published 1 a 

 suggestive paper, which will be perused with much interest 

 by those engaged in the study of rocks, and may possibly call forth 

 a few remarks or further observations on some points discussed in 

 the paper 2 ; the object of the author being to consider the value of 

 some of the distinctive characters which are generally accepted at 

 the present time in defining certain kinds of rocks. As some of our 

 readers interested in petrology may not have ready access to the 

 original communication, we have reproduced the summary, by 

 Prof. Dana, of the principal points with regard to rocks which 

 have been brought out in this paper, together with his proposed 

 classification of the crystalline rocks. 



" 1. The necessities of the science of Geology constitute the most 

 prominent motive for distinguishing hinds of rocks ; and they should 

 determine to a large extent upon what characters distinctions should 

 be based. 



1 Amer. Journ. of Science and Arts, vol. xvi. Nov.-Dec. 1878. 



2 See Article in the present Number, by Prof. Bonney, M.A., F.E.S., ante, p. 199. 



