488 SROART MVE EEE Ke 
Devonian material is not continuous forany great distance back 
from the quarry face, as will be seen in Fig. 3, this figure being 
a view taken nearly at right angles to that shown in Fig. 1, 
after the rock to the right of the opening against which the 
hammer leans in Fig. 1, has been removed. The Devonian mate- 
rialin the figure is the darker rock above and to theright of the 
hat, the line of demarcation between it and the limestone above 
being sharply defined ; it is seen to thin out rapidly back from 
the quarry face. 
At the base of the triangular opening, between the two beds 
of limestone that come in contact at that point, the Devonian 
“material extends both to the right and to the left for several feet, 
forming a bed an inch or two in thickness between the two lime- 
stone beds. This bed has every appearance of having been depos- 
ited upon the lower limestone bed before the upper one was 
laid down, but in reality it was deposited at a much later date in 
a cavity which existed there near the close of Devonian time. 
The sort of unconformity presented by this occurrence of 
Devonian sediments deeply buried in the Niagara limestone is 
peculiar. No description of any similar occurrence has been 
observed in the literature, and it may be designated by the name 
subterranean unconformity. 
STUART WELLER. 
THE UNIVERSITY OF CHICAGO. 
