184 



THE WORt.C. 



some internal agency, the various formations, or beds of nearly 

 the same character, will OCCUP in contrary Order, thus, suppose 

 that by an upheaving cause, a series of strata, fig. 1, lying orig- 







inally horizontal, as deposited at successive epochs, by water, to 

 be, by some internal force, upheaved as in fig. 2, the external 



surface being rent and cracked, and further that after a course of 

 ages, the softer and more modern deposits should be worn away 

 by the agency of rains, frosts, floods, &c., until it was reduced to 

 the level a b, we would have the succession of strata as in fig. 3, 



the harder rocks, perhaps of granite, forming a nucleus, or cen- 

 tre, around which the rest would lie in order; perfectly circular if 

 the elevation had been a true mound, or arranged in lines parallel, 

 or curved, according to the nature of the original elevation, and 

 if the elevation and subsequent denudation, had occured at a very 

 remote period, the whole might be covered with a light loose soil. 

 A very pretty and instructive example is shown in the diagram 

 on the next page, which is an outline map of Michigan. 



Here the centre of the state is occupied by the coal measures 

 or formation, shown by the shaded portions, skirting this i a nar- 

 row stratum of limestone, beyond this and circling around it, is a 



