J 42 REGINALD A. DALY 
observation by Garwood that some of this substance must be 
present if a limestone concretion is to grow large, although his 
analyses show that more than 30 per cent. of that carbonate 
seems to prevent the concretionary process.! 
In all cases the structure is typically radial throughout the 
concretion, except at the rather indefinite small core of massive 
crystallized lime carbonate, which can usually be seen at the 
center. I have found no organic center of concretion, and no 
center other than calcite in any specimen. The free ends of the 
radiating crystals present the characteristic cleavage-planes of 
calcite, and the curved surface of the sphere is otherwise indented 
only by the faint depressions where the latter was in contact with 
the layers of shale (Fig. 5). Lastly, there is often to be seen, 
in addition to the radial structure, a concentric banding in the 
_ split-open sphere, a layering that seems to be original and con- 
nected with varying conditions of growth (Fig. 6). 
The most important problem in connection with these con- 
cretions doubtless adheres to the question as to how the strata 
came to be deformed on all sides of each spheroid. That very 
considerable mechanical energy has been expended in the process 
is evident, not only in the development of a dome over the upper 
hemisphere and of a cup holding the lower hemisphere, but also 
in that of a sort of slaty cleavage, which can sometimes be ‘dis- 
cerned in the shale adjacent to the equatorial zone (Fig. 5). 
What is the source of the energy? 
One of the first explanations that suggested themselves to 
me consisted in referring the deformation of the beds to differ- 
ential movements in the strata as these adjusted themselves 
to the loss of water, and to the ensuing consolidation of the orig- 
inal muds to shale. The concretion itself would not lose bulk in 
such a case, and the layers overlying would be supported at the 
upper pole of the spheroid, while there would be less and less of 
such support for the same strata along lines radiating from the 
pole in the horizontal plane, until a maximum of instability would 
be reached outside of the equatorial circle. Here there would 
tGeol. Mag., 1891, p. 439. 
