J. L. Campbell— Geology of Virginia. 441 
undermining the harder strata. The most conspicuous irregu- 
larity has been caused by the undermining of the interstrati- 
sometimes wavin , and to cause a mass of it to slip from 
its normal position and modify both dip and strike, as seen just 
above the margin o canal. This seems to me the only 
stone, but the aggregate must be at least six hundred feet. 
Number 4 is not well defined below, since 3 becomes more 
part of it is a bed of brownish gray sandstone with a we 
defined upper surface. It crosses the river at the Cement Mills, 
and its highest ledge forms the abutment of the dam on the 
opposite side of the river. Where a deep channel was washed 
out by a freshet a few years ago, this rock is well exposed on 
the lower margin of the turnpike, and its upturned edges may 
be conveniently examined. A considerable exposure of it 
also crops out above the turnpike between the houses of Messrs. 
Locker and Campbell, while the corresponding ledge may be 
seen on the cliff beyond the river. It has a very regularly 
jointed structure—the cleavage planes being so distinct as to 
ave been mistaken by an unpracticed observer for planes of 
stratification dipping to the southeast, while the true planes of 
stratification dip with considerable uniformity and great con- 
stancy toward the N.W. n 
_ In this and some of the lower beds of sandstone, very faint 
impressions of fucoids and occasional Scolithus borings are 
found; but the conglomerate structure is much less prominent 
here than in the older 
