

CALCIFEROUS SANDROCK. 105 



intensity of tlic forces by wliicii they were transported. In some places, therefore, they are 

 coarse, and irregularly mingled ; in others, they are fine, but in large quantities, and appear 

 to have been borne along by a moderate current, which has given a diversity in the stratifica- 

 tion resembling that of inclined beds, or beds which have been elevated subsequent to their 

 consolidation, as in the annexed diagram, fig. 33. Phenomena of this character are common 



to all accumulations of gravel and sand, but do not 

 i become evident in any of the argillaceous or calca- 

 3 reous rocks, probably in consequence of the extreme 

 M fineness to which the particles are reduced. Among 

 -^ other phenomena, ripple marks may be seen through- 

 out the whole of the rock, when the materials were 

 not too coarse ; showing that during the period when 

 this deposit was in progress, the waters were quiet, 

 and free from those disturbances which give origin 

 to a confused stratification. 



Fossils. — The Potsdam sandstone is extremely poor in fossils ; but it is interesting to find 

 even a single bivalve shell, thus setting aside the former crude notions in relation to the order 

 in which beings were created. The only distinct and well characterized fossil of this rock, is 

 the Lingula ovata, found abundantly at the High bridge near Keeseville. It is small, very 

 thin, and rather obscure. It is also found in the same rock at French creek, about one mile 

 east of the village, in a friable variety of the rock. Besides this fossil, another resembhng 

 the Fucoides demissus of Conrad, occurs between Wilna and and the Natural bridge in Jef- 

 ferson county : it is not characteristic of the rock. 



2, Calciferous Sandrock. 



Mixture of earthy and calcareous matter. — Presence of Calcareous Spar. — Geodiferous. 



As its name indicates, it is a sandy limestone : it is not, however, destitute of beds of pure 

 limestone. The mixture of a variety of mineral matter causes the rock to weather unequally ; 

 hence it is often rough externally, portions of the siliceous part standing out in relief. This 

 rock is not uniform in its appearance, although there is in general a peculiarity whicli distin- 

 guishes it from the other rocks of this group. There are two quite uniform characters which 

 may be oliserved in the calciferous, viz. a fine crystalline structure, intermixed with earthy 

 matter, and numerous small masses of calcareous spar. A section will best exhibit the usual 

 order of the varieties which compose it, and which I have placed under this name. 



Geol. 2d. Dist. 14 



