40 



STRATIFIED ROCKS. 



IJrrER 



Gallery. of lime > and others of two or more of these materials, mixed 

 Waii^e4i. in evei 7 Possible manner. Some strata are formed almost 



exclusively of organic remains, as, for instance, in the case 



strata, (No. 173, Wall- 



of the oyster bed in the Purbecl 



Wall 



) 



Specimen 32, in 



s 



bed of Carboniferous limestone, in which, in South Pembroke- 



shire, there are 500 feet of strata formed almost exclusively 



of the remains of Ericrinites. 



The manner in which strata are now deposited is easily 



applicable to all the formations from which the rock speci- 

 mens (Cases 41 and 43) have been derived; and in lib* 

 manner, the study of the rocks themselves, in situ, re-act. 

 in giving clearer conceptions of the manner by which great 

 rocky deposits are now being formed. From this we learn, 

 for instance, that ripple marks and sun cracks, (see specimens 

 179, 180, 181, 182, 183, 188,) made in the interval between 

 high and low water mark, are, under favourable 

 stances, sometimes preserved and fossillized. The same is 

 the case of the foot-prints of animals that walked along the 

 beach, (see slabs in opposite gallery,) and in innumerable 

 instances plants, land, fresh-water, and marine shells, crus- 

 taceans, fish, reptiles, birds, and mammals, sometimes of 

 living but chiefly of extinct species, have been perfectly 

 preserved. — A. C. Ramsay. 



circum- 



Specimens illustrative of the structure of Conglo- 

 merates and Breccias, Grits, Sandstones, Sands, 

 Shelly and other Calcareous Sands, Marls, Clays, 

 Shales, Slate, Coal ; and of Ripple and Current 

 Marks, &c. on Old Sea Bottoms. 



Arranged and described by H. W. Bristow. 



1.— Conglomerate from the Great Oolite, composed of 

 rounded fragments of slightly oolitic limestone in a base of 

 calcareous matter.— Stow-m-the- Wold, Gloucestershire. (See 



" Memoir on Geology of Mao 44." bv Edward Hull. n. m.} 





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