Sect. VI.] 



GEOLOGY. 



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If at the bottom of a cliff, say 800 feet in height, a set of 

 shells are burled, which must have lived under water 

 only 50 or 100 feet in depth ; it is clear that the bottom 

 of the sea must have sunk to have allowed of the deposi- 

 tion of the 700 feet of superincumbent submarine strata x 

 subsequently the whole 800 feet must have been up- 

 raised. For this same purpose, and for other ends, it is 

 desirable that it should be noted which species are the 

 most numerous, and whether layers are composed exclu- 

 sively of single kinds. It should be also remarked, whe- 



bivalve shells retain their two 

 valves united, and whether the burrowing kinds are em- 

 bedded in their natural positions, as these facts show that 

 the shells have not been drifted from afar. Where there 

 are fossil corals, it should be observed v/liether the 

 greater number of specimens are ujjright, in the positions 



in which they grew. The remark formerly made that 





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the collection of mere fragments of rock is of little or no 

 use to geology, is far fi-om applicable to fossil reniaii.^. 

 Every single fossil species, bones, shells, Crustacea^ 

 corals, impressions of leaves, petrified w^ood, &c., should 



be collected, and it is scarcely possible to collect too 

 many specimens. Even a single species without any i r 

 formation of any kind, if it prove a quite ne'w form, will 

 be valuable to the zoologist; if it prove identical with, or 

 closely allied to a known species, it may interest the 

 geologist. A set of fossils, however, and still more 

 veral set?., with their superposition known, cannot fail 

 ^" of the highest value ; they wdll tell the age of the 

 deposit, and perhaps give the key to the whole geology 

 of the country: some of the highest problems in thi 



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