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GEOLOGY, 



[Sect. VI. 



shells, \ 



,vhicn have hceii exposed for many ages, yet retain 

 their colours in a surprising manner. The very hest evi- 



dence is afforded by barnacles and boring shells being 

 found attached to or buried in the rock, in the same posi- 

 tions in which they had lived ; these may be sometimes 

 found by removing the earth or birds' dung covering points 

 of rock. Where shells are embedded in a superficial layer 

 of soil, though it may appear exactly like vegetable mould, 

 specimens of it should be preserved, for the microscope 

 will sometimes reveal minute fragments of marine animalg. 

 In ail these cases, specimens of the shells, though broken 



to 



and weathered, and having a wretched appearance 



J 



must 



carefully be preserved ; for a mere statement that such 

 upraised shells resembled those still living on the beach is 

 absolutely of no value. It should be noticed whether the 

 proportional numbers between the different kinds appear 

 to be nearly the same in the upraised shells and in those 

 now cast on the beach. The height at which the marine 

 remains occur above the level of the sea should be mea- 

 sured. In confined situations where the change of level 

 appears to have been small, much caution must be exer- 

 cised in receiving any evidence ; as a change in the direc- 

 tion of the currents (resulting from alterations in neigli- 



s 



bouring submarine banks) 

 omewhat less height, and 

 the land having been upraised. 



US 



the appearance of 



\\ herever a tract of country can be proved to have 

 been recently elevated, its surface, as exhibiting the late 

 action of the sea, is a fertile field for observation. On 



«ncl 



1 coasts, terraces rising like steps, one above another 



often occur. Their outline and composition should 



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