COAL FIELDS. 251 



the accumulation of which must have required a 



long period of years. But they also show traces of 



1 volcanic action, in the " dikes and cutters," by which 



j they are intersected, and which often throw the 



I strata out of the plane, so that the coal is higher on 



I one side of the dike than on the other. Those 



dikes are frequently " whinstone," or allied to ba- 



; salt ; and there are cases in which the basalt has 



' issued in quantity and formed " caps" on the top of 



| the other strata. The coal-field in the south of 



! Fifeshire is remarkable for those caps, which there 



form very beautiful conical hills, locally termed 



" laws." The top of one of these, " Kellie law," is, 



under the 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- 



