108 NEW YORK STATE MUSEUM 



is of the type of the cross-bedding structure in sandstone. Such 

 structure indicates that the bed possessing it was a fine calcareous 

 sand, subject to shifting movements by waves and deposited in 

 moderately shallow water. We need look for organic remains in 

 such a rock with no more assurance of finding them than we bring 

 to the examination of uniform bedded shales. They may be abun- 

 dant or they may be rare or absent altogether. Thus a limestone 

 need not be necessarily a fossiliferous rock. 



Geodes of the usual type are common, the dolomitic lining pre- 

 dominating. 



7) On the preceding thin stratum follows a limestone mass of very 

 uniform character, hardly separable into district strata, though con- 

 sisting of numerous beds. 1 27 feet of this stratum are shown at the 

 quarry near the northern end of the section, where the upper ex- 

 posed bed forms the surface rock of the plateau above. The beds- 

 are generally of considerable thickness, but the fine stratification 

 structure is not so well marked as in the strata below. The rock 

 may be considered a compact granular dolomite, in which consider- 

 able change has taken place since its original deposition. It is of a. 

 grayish color but weathers to a lighter tint. Geodes are plentiful, 

 often quite large, and in these, minerals of great beauty are not infre- 

 quently found. The most common are the snowy variety of gyp- 

 sum or alabaster, the darker gray, massive, fine anhydrite and the 

 uniform, fine, dolomite rhombohedra with curved faces, generally of 

 a pinkish tint and familiarly known as pearl spar. Long slender 

 crystals of calcite, generally in the form known as scalenohedra, or 

 dogtooth spar, are not uncommon. These are commonly of a 

 golden color, and large enough to show well their crystal faces. In 

 the new power tunnel which was excavated in the neighborhood of 

 the falls, large masses of transparent gypsum of the selenite variety 

 were found in cavities in this rock. Some of these pieces were 6 

 inches in length. Masses of limestone lined with pinkish dolomite 

 crystals and occasional large masses of silvery selenite, and set with 



^The distinction between stratum and bed is an important one. A stratum 

 is a rock mass having throughout the same lithic character, and may be 

 thick or thin. A bed, on the other hand, is that portion of a stratum limited 

 by horizontal separation planes. See Geology and paleontology of Eighteen. 

 Mile creek pt 1. Introduction. 



