Outlines of Geology, 87 



themselves according to the individual strata which they occupy. 

 Lastly, in the uppermost and superficial strata, we find shells, not, 

 as in former cases, changed, petrified, or lapideous, but in such a 

 state, that when washed and cleaned, they might pass for recent ; 

 some of these correspond to marine shells, and others, in other 

 strata or beds, resemble our present fresh-water shells ; whence 

 the alternate inundation on certain spots of fresh and salt water 

 has been inferred. In the most superficial and highest of these 

 strata, we at last arrive at shells such as now exist, and then 

 comes that great tell-tale of the deluge, the gravel, in which we 

 discover the remains of land quadrupeds of unknovm genera, and 

 of extinct species, and, commonly, the latter correspond to inha- 

 bitants of very different climates at present. 



Another important circumstance upon which I have only slightly 

 touched, is the very frequent occurrence of rounded pebbles com* 

 posed of fragments of the older rocks, which are abundant in th^ 

 secondary strata. These pebbles prove the antecedent formation 

 and consolidation of the rocks of which they are the debris ; and 

 they also shew another curious fact in the history of stratification, 

 which is, that where they occur, as they often do, in vertical 

 beds, they must have acquired that verticality by the operatiou 

 of some force which has thrown them out of their original hori* 

 zontal position ; for we cannot suppose it possible that any exteft" 

 sive accumulation of loose gravel can have taken place upon sur* 

 faces greatly inclined to the horizon. 



Such beds of consolidated gravel are common in the red sand- 

 stone below the carboniferous series, in that series in the lower 

 strata of the superior red sandstone, in the sand below the chalk, 

 and in the gravel immediately above it and below the London 

 clay. 



Now it is impossible to contemplate the collection of marine 

 relics which are so abundant in many of the strata, and which are 

 found upon the summits of some of the loftiest mountains of the 

 world, without immediately coming to the conclusion that our 

 present land has not been merely transitorily covered by the 

 waters of an inhabited ocean, but that it has actually been 



