CALCAREOUS GONGCRETLON S| OF GELTELE iP OLND, 4VA3 
be a maximum of collapse which means, in the end, a doming 
above the upper hemisphere. I have found that the same 
explanation had been brought forward by both Newberry’ and 
by Rominger.? But it leaves out of account the structural cup, 
which holds the lower hemisphere, and which is just as well 
developed as the dome overhead (Fig. 3). Moreover, the exist- 
ence of the concretion before the act of consolidation is not 
considered; yet we must believe that a theory of the deforma- 
tion should be controlled by the recognition of the fact that many 
cubic feet of the shale must be displaced to permit of the growth 
of the larger concretions. We know of no reactions by which 
replacement of argillaceous material by slow molecular inter- 
change with carbonate of lime may take place, nor can we con- 
ceive of such large spherical and spheroidal cavities as those 
necessary for the segregation of the calcite as having antedated 
the segregation. The last supposition is particularly invalid, 
for, in any case, it would leave the radial structure unexplained. 
The same objection may be made to the hypothesis that 
energy sufficient for the deformation of the strata might be forth- 
coming in the process of forming a pseudomorph of calcite after 
some other carbonate of greater density. Siderite does, indeed, 
occur in radially concretionary form in the Black Shale of Michi- 
gan. But, while there might be an important increase of volume 
with the application of expansive energy analogous to that ensu- 
ing on the change from anhydrite to gypsum, we have still to 
account for the original displacement of the shale to make way 
for the siderite or other earlier carbonate itself. It may also be 
stated that the disturbance of the shale is visibly greater than is 
possible on a mere change of volume in the pseudomorphosing 
reaction. 
There thus seems to be no escape from the conclusion that 
the crystallization of each concretion and the opening of the 
‘Op. cit., p. 155. AO} Cilin, [Bs GG. 
3 NEWBERRY’S largest concretion of the sort here described, and occurring under 
similar conditions, measures 10 feet in diameter, giving a volume of more than 500 
cubic feet. Geology of Ohio, 1873, p. 155. 
4Geol. Surv., Mich., Vol. III, 1873-1876, p. 67. 
