94 
GEOLOGY OF THE FOURTH DISTRICT 
30 . 
Curved strata — Porter’s quarry, Niagara Falls. 
The woodcut represents the strata as they appeared, looking in the direction south by east, 
and against the edges of the layers, which are crossed by vertical joints, having a direction east 
by north and west by south. The extent of each curve is from one to two feet; sometimes a 
single one divides and forms two. There is here no evidence of a breaking up of the strata 
below, and consequently there has been no uplifting process to produce these curvatures. It 
appears rather due to the accretionary force, which induced a tendency to curving or folding 
in the laminae throughout the mass, operating with great uniformity and over a wide extent. 
These curves seem due to like causes with those small ones at Lockport, which are usually 
less than one inch in diameter. 
There seems no reason to doubt that all these appearances are due to the same action which 
produces well-defined concretionary forms in other situations, and under more favorable cir¬ 
cumstances. The oolitic and concretionary character of this formation in some parts of the 
Third District, seem to be represented in a great degree by what is here exhibited in the 
terminal strata. 
The same structure exhibited in the two last illustrations occurs in the Third District, as 
illustrated by the following woodcut from Mr. Vanuxem’s Report: 
