30 GEOLOGY OF THE THIRD DISTRICT. 



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2. CALCIFEROUS GRT 



Calciferous Sandrock, and Transition Sandrock of Eaton. 

 (No. 2. Pknnsylvania Survbt.) 



Tlic terra Calciferous sandrock, as it does not comprehend all the masses of the district 

 which are synchronous with it, the more comprehensive word group is now used. It em- 

 braces, generally, three distinct masses, as to character and position. These alternate and 

 intermix with each other. 



The first is siliceous, compact, and may probably be the continuation of the Potsdam sand- 

 stone, either in part, or almost wholly. 



The second is a variable mixture of fine yellow siliceous sand and carbonate of lime, which, 

 when fractured, presents a fine sparkling grain. It is in layers, but they rarely show that 

 very regular structure which usually belongs to a limestone rock. They have a shattered 

 appearance from numerous cracks, the parts being more or less separated from each other. 

 This is the mass from whence the name calciferous sandrock was derived. 



The third is a mixture of the calciferous material, which is usually yellowish, very granu- 

 lar and sparkling when fresh broken, and of compact limestone, which resembles the birdseye 

 limestone in its mineral character, containing also some argillaceous or slaty matter. These 

 materials often have the appearance of having been deposited in thin alternate slaty layers, 

 but more or less intermixing with each other, the birdseye appearing to have been passive 

 when aggregating, whilst the calciferous particles, on the contrary, were active, shooting into 

 ramose forms, which might be confounded with the fucoids which are found with these layers. 

 The action of the weather upon these layers is very peculiar, giving to them, after long expo- 

 sure, the appearance of gothic fret work, and in the district are characteristic of this rock. 

 The color also becomes a dark yellowish brown. These materials are often associated and 

 coated over with a greenish slate or shale, which sometimes is oclirey by alteration, and are 

 the bark-like layers of the late Prof. Eaton ; tlie whole mass having been designated, in the 

 annual report, by the name of Fucoidal layers. 



In the annual reports, the fucoidal layers were separated from the calciferous sandrock, in 

 consequence of always observing that they were above the great mass of the latter rock ; 

 overlooking the fact, as it appeared to be of little importance, that the fucoidal layers were 

 alw^ays covered by a few or more layers of the calciferous rock. A re-attention to the subject 

 was caused by the observations of Dr. Emmons in the second district, where the mass above 

 the fucoidal layers is greater than the one below it ; the combined observations of the two 

 districts showing that the two constitute a group, in which the fucoidal layers are included, 

 and therefore a subordinate mass. Though these layers are made up generally of parts 

 which are thin, they are often in layers of two or even several feet in thickness, and of con- 

 siderable regularity, and by this character are readily distinguished from the layers of the 



