1884. ] Opinions upon Clay Stones and Concretions, 889 
In the special instances of concretions known as clay stones— 
carbonate of lime, clay, sand and iron—two writers have treated 
of them at considerable length. Parrot, in the Memoirs of the 
Academy Sciences St. Petersburg, Vol. v, 6th series, gives a very 
extended examination of the stones of Imatra, which ends very 
inconclusively with assigning them to an organic origin. His 
figures are very interesting, and differ considerably from the 
familiar forms of the Connecticut valley. 
Professor Hitchcock, in the Geology of Massachusetts, devotes 
considerable time to them, and his remarks are most important. 
He considers them as formed by the crystallization of calcite in 
clay, that lateral accretion predominates, from the easier movement 
in the clay particles sideways, that different localities have different 
forms, and that they are laminated by growth from segregation 
in successive layers of the clay bed. He seldom finds nuclei. 
The writer’s examination of a collection of these objects seems 
to warrant the following conclusions: 
_ Ist. That in their formation they have passed through a pre- 
liminary or soft stage, before hardening, more or less long (Pl. 
XxvI, Fig. 7; Pl. xxvii, Pig. 1). 
2d. That the process of a concretion has formed a center about 
which others gathered; has, as it were, precipitated and induced 
More extended action of the same sort (Pl. xxvi, Fig. 5). 
_ 3d. That the approach to solidity of a concreting mass is 
attended with a development of new centers around which con- 
cretions form (PI, xxvii, Figs. 7-8). 
4th. That the tendency of matter is to concrete around a center 
from all sides equally, but that if there is deficiency of material, 
on the side where the material is plentiful, the form will corre- 
spond (Pl. xxvi, Figs, 2, 5, 6). 
5th. That concretions lie parallel to the bedding, are flattened 
vertically, are wider than high (Pls. xxvi, xXXVv11). 
6th. That the upper surfaces are varied and in relief, while the 
bottoms are apt to be flat (Pl. xxvu, Fig. 8). 
7 th, That the concretion is often plainly built upwards by the 
“uperimposition of many films (Pl. xxvut, Figs. 2, 3, 6). 
8 - That the amount of carbonate of lime varies: according to 
Hitchcock, 43 per cent to 56 per cent; Parrot 51 per cent to 55 
Per cent; Swedish, 60 per cent to 61 per cent; the writer, 45.63 
Per cent, 
