Concretionary Carbonate of Lime. 



181 



these plates, or a congeries of the spheroids, exceed that of a single 

 layer of the clay, which is rarely more than half an inch. 



On breaking these concretions they are found to be perfectly solid 

 and compact ; exhibiting in no instance the slightest marks of concre- 

 tionary structure, such as we see in the oolite. Nor could I bring to 

 light a concentric arrangement of the materials by applying the heat 

 of a blow pipe, even till the surface was fused. Generally, however, 

 the heat of a lamp alone will cause them to burst asunder with con- 

 siderable force. The mass is obviously composed of carbonate of 

 lime mixed with clay, such as that in which they are found, consist- 

 ing of alumina and fine sand, with occasional fine scales of mica. 

 The hardness of the concretion is about the same as the common im- 

 pure compact limestones. It does not constitute any considerable 

 part of the stratum in which it is found; I have observed it in Am- 

 herst, Hadley, South Hadley Canal, Chicopee in Springfield, Green- 

 field, &c. ; also in the clay beds along the river Hudson, near Albany. 



I have been thus particular in this description, because I have met 

 with but one account of any similar production in any tertiary strata. 

 It is obviously an example of the solid concretionary structure, and 

 must have resulted from chemical agencies. But are concretions the 

 result of crystalographical laws ? If so, why are not crystals pro- 

 duced ? It seems to me that philosophy is yet in the dark on this 

 subject. At first it occurred to me that these concretions were the 

 oolite in a forming state ; and that the consolidation of the clay would 

 develope a concentric structure. But my failure to bring this to light 

 by the application of heat, convinced me that the opinion is unten- 

 able. 



The single account of similar concretions referred to above, is 

 that of Cuvier and Brongniart, in their description of the Paris Ba- 

 sin. " We find," say they, " towards the surface of that bed of clay, 

 (the Plastic Clay,) masses as large as the head, though often much 

 smaller, of nearly compact limestone, or made up of small compact 

 nodules, aggregated together as if by concretion. These masses of 

 limestone have their edges blunted and their angles both salient and 

 rentrant rounded, as if they had been plunged into a liquid sol- 

 vent."* 



Quite recently I have found in the gray argillaceous sandstone at 

 Sunderland cave, in Mount Toby, numerous reniform concretions, 



* Recherches sur les Ossemens Fossiles, par Cuvier, Tome % p. 341. Paris, 1825*. 



