LIMESTONE AND MARBLE. 265 



green sod, as regular a basaltic pavement as the 

 top of Staffa. 



We may, by the observation of what we see 

 going on at the surface of the earth, understand 

 how a bed of sand, clay, or gravel is formed ; and 

 there are instances in abundance of the formation 

 of peat-bogs. In those cases we can also in 

 general tell whether the bed has been formed in 

 a pool, or by an occasional fall of rain, or flood. 

 But when we look at even a very limited portion 

 of the tamest country, we are utterly unable, by 

 any power of which we can see or imagine the 

 working in the air to account for the form of its 

 surface. The gravel and clay hills, near London, 

 again occur as the most familiar instances, though 

 they are far from being the most striking ones. 

 Water, whether of the sea or not, must at all times 

 have preserved its level, because that is the very 

 constitution of its nature, and without that it could 

 not have been water. The currents of the sea 

 may have done a little, but it could be only a 

 little ; for it does not appear that even the gulf 

 stream of America rolls stones before it ; and the 

 little coral insects are quite competent to the task 

 of erecting a wall from the unfathomable depths, 

 sufficient to stay the roll of the wide Pacific, even 

 in its most stormy latitude, and with a tide-run 

 of several thousand miles. So that those minor 

 operations of these internal fires of the earth are 

 necessary to account for the inequalities of the 

 surface, which are not formed of rock but of 

 accumulated fragments. 



They also enable us to account for the formation 

 of beds of chalk, and shelly limestone, and marble 

 in all their varieties of form. 

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