TRENTON LIMESTONE. 293 



in lieu of those that have already found a place in the literature of 

 M'estern geology. 



It is not presumed that the distinctions here made have any wide 

 geographical application, and hence the terms in common use have 

 only received such qualification as the geology of this region demands. 



The term beds has been substituted for limestone, since, in tha 

 opinion of the writer, these divisions do not rise to the dignity of 

 what are technically known among geologists as epochs, to which 

 grade the more significant term should be confined, unless there are 

 special lithological reasons for its use otherwise. While it is very 

 much in the interests of science, and its practical application, to sub- 

 divide the several formations as far as the facts will permit, and thus 

 give to our discriminations and descriptions as much of exactness as 

 possible, much confusion is introduced into the general literature of 

 the science, if each of these minor members is clothed with a formal 

 title. 



/. The Lower Buff Beds. It has already been observed in connec- 

 tion with the St. Peters sandstone, that a slight alternation of sand- 

 stone and calcareous layers occurs in the transition to the Trenton 

 limestone, there being above the main body of sandstone a calcar- 

 eous layer of about four feet thickness, overlaid by a bed of sand- 

 stone two feet or less in thickness. Above this there follow the 

 Lower Buff beds. Their usual thickness is from eighteen to twenty- 

 five feet. At some points the formation seems to be made up of 

 three main strata, the lower one, more or less shaly toward the bot- 

 tom, of about four feet thickness, the middle one seven feet, and the 

 upper, twelve. These are less distinctly subdivided into beds from 

 two feet in thickness downwards. "When these distinctions are not 

 observable, the layers are of a similar heavy bedded character, except 

 when affected by the action of the elements. The texture is some- 

 what irregular, arising from an uneven association of earthy and 

 crystalline material. The general aspect is earthy, but crystalline 

 particles compose the greater part of the mass. The color, as seen in. 

 natural ledges and superficial quarries, is a light yellowish'buft' or 

 gray. The interior of thicker and less exposed layers frequently has 

 a bluish cast. 



The rock is composed of carbonate of lime and magnesia, a con- 

 siderable percentage of silicious and aluminous material, and an in- 

 significant ingredient of iron and the more common salts. Crystals of 

 calcite and occasionally those of pyrite occur in cavities. 



The fossils of this division are abundant, although less so than in 

 the upper divisions, especially the blue beds. 



