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DESCRIPTION OF THE PLATE. 
We are indebted to Photography for enabling us to 
represent the remarkable slab from Greenfield, and its 
numerous objects, in a small space, yet with perfect 
accuracy. This slab is four feet seven and one-half 
inches in one direction, and four feet one inch trans- 
versely to this; in thickness it measures about an 
inch. It is composed of gray sandstone, in which 
the micaceous element is conspicuous, and contains 
many interesting impressions on both surfaces. 
The most interesting surface is the inferior; and 
the objects are, of course, presented in relief. They 
are, first, two Chelonian tracks; second, four sets of 
bird-tracks ; third, footsteps of an unknown animal. 
The Chelonian tracks are two in number: the longest 
measures four feet ten inches; the shorter, two feet 
nine inches. Both of these impressions are made 
apparently by the plastron of the turtle. They are 
from four to eight inches in width, and composed of 
elevated striae. These striee are formed by raised lines, 
pursuing a course generally regular, but accompanied 
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