270 



CALCIFEROUS SANDKOCK. 



the ledge of sparry limestone at Birchard's saw mill, a great ledge fifty feet high with a perpendicular 

 western wall upon the east side of the Lemonfair ; also the ledge of limestone with a westerly dip near 

 H. DeLong's house both in the northeast part of Shoreham. As this rock joins upon the rnetamoiphic 

 limestones to the east, its eastern boundaries have not been ascertained with accuracy ; especially as the 

 true place of the latter upon the geological scale was not made certain till after the completion of the 

 field work of this region. 



In the south part of Addison commences the third range of calciferous sandrock. It is seen in place at 

 the west foot of Snake Mountain, dipping from 10 15 E. It is composed of two varieties, the lower 

 layer is quite silicious and the upper layers are thick-bedded like the Chazy limestone at Vergennes. The 

 amount of the whole is inconsiderable. We have found the calciferous sandrock in place nowhere else, ex- 

 cept near the Elgin Spring, in Panton, where it closely resembles the Potsdam sandstone, so much silica 

 is there in its composition. The rock dips slightly to the east. 



These ledges are situated upon a sort of table land, about 250 feet above Lake Champlain. The village 

 of Addison is upon the same elevation. As the rocks in this vicinity are almost entirely covered with clay, 

 FlQ 170< it is difficult to determine the boundaries of the various formations. If 



there is an uplift of all the lower silurian rocks west of Snake Mountain, 

 the west edge of this terrace is the western limit of the calciferous. If 

 not, then this rock probably extends one or two miles westward. Its 

 northern limit is ascertained to be south of Vergennes. 



In the west part of Panton, the amount of the formation is very small, 

 not sufficient for the map. It deserves notice, because it indicates that 

 small disturbances among these lower silurian rocks are quite common. 



The thickness of the calciferous sandrock in Vermont was estimated 

 at 300 feet, by Prof. Adams. We should estimate the thickness the 

 same. This corresponds with its general thickness in New York. 



The minerals are not numerous in this member. Occasionally good 

 specimens of different colored calcites, in different crystals of transparent 

 and fetid quartz and fragments of bituminous coal, occur in it in Ver- 

 mont. 



Fossils. Quite a large mumber of species of fossils have been found in 

 the calciferous sandrock in North America. We have collected for the 

 State Cabinet, from Vermont, only four or five species of organic re- 

 mains, concerning which we can speak with confidence. They are a 

 species of Palccophycus, Maclurea matutina (Hall), M. Sordida (Hall), 

 and a species of Ophileta. 



Fig. 170 represents, poorly, a part of a large specimen of a species of 

 Palaeophycus from the fucoidal layer at Mount Independence, in Orwell. 

 Its position therefore, is at the base of the calciferous sandrock. The 

 stone is terete, simple or branched, cylindric or subcylindric ; the surface 

 is nearly smooth, without transverse ridges, and was apparently hollow. 

 These plants and others like them, scattered through this rock, are un- 

 doubtedly marine. They seem to have been large, succulent stems, 

 perhaps hollow, like certain algae. 



It is common to find other traces of plants in the calciferous sandrock 

 in Vermont, in the occurrence of numerous small bunches of bituminous 

 matter. Of course it is impossible to derive, from these fragments, any 

 specific information relating even to the generic character of the plants 

 from which the bituminous matter was derived. So abundant is this vegetable matter in some localities 

 as to impart a nearly black color to the rock. 



Palseophycus. 



