1899] wa ROCK OUT OF PLACE 315 
A Rock out of Place. 
Iy the July-August number of the Journal of Geology (vii. pp. 483- 
488) Stuart Weller describes the peculiar occurrence of a small patch 
of Upper Devonian rock in the heart of a quarry of Niagara limestone 
at Elmhurst, Illinois. At this locality the limestone is much fractured, 
and one of the joints is enlarged to form a cavity, triangular in section, 
6 inches wide at. the base and 16 inches high, but thinning out as it 
passes into the rock. This cavity is filled with angular fragments of 
the adjacent limestone embedded in a dark brown sandy matrix, which 
contains fish-teeth, Lingula, and other brachiopods, the total suggestive 
of a late Devonian age. From this material two new species of 
Diplodus are described by C. R. Eastman in the samme number of the 
Journal. Further, says Dr. Weller, “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 left 
for several feet, forming a bed an inch or two in thickness between the 
two limestone beds.” 
The nearest outcrop of Devonian is 80 miles from Elmhurst, so that 
the position of this patch is doubly interesting. Dr. Weller explains 
it thus. During the greater part of Devonian time the region must 
have been above sea-level (an inference which seems to follow 
legitimately from the alleged age of the deposit). “The waters which 
collected upon this land surface in part percolated through the under- 
lying rock strata and by solution increased the size of many joint 
eracks. Ata later period, near the close of the Devonian, when the 
sea again occupied the region, sand was sifted down into these open 
joints, and with it the teeth of fishes which inhabited the sea there- 
about.” The opening was, “ perhaps, large enough for the entrance of 
some of these fishes.” Traces of the same sandy material are seen on 
the joint-face above the opening. 
If this explanation be true, then, as Dr. Weller phrases it, “no 
description of any similar occurrence has been observed in the 
literature”; but this scarcely justifies the conclusion of the sentence, 
“and it may be designated by the name subterranean unconformity.” If 
the mode of occurrence were at all common, if it were anything but 
unique, then perhaps a name might be convenient. At present there 
seems no advantage in one. Moreover, we are not convinced that Dr. 
Weller’s account is the true one. It does not allude to the occurrence 
of clay in the other joints, and it affords no explanation of the lime- 
stone breccia. Can Dr. Weller prove that this is not a fault-rock, in 
which fragments of the immediately adjacent rock are mixed up with 
fragments or washings that have fallen down the crack from the super- 
jacent rock? Such an occurrence is common enough, though we know 
no technical name for it. 
