POTSDAM SANDSTONE. 265 



the railroad the clip of the older rock is 36 E, and only a few rods east the dip of the sand- 

 stone is only 9 E. As the south point of West Haven terminates in a cliff, this section can be 



lcg distinctly seen from quite a distance. The 



rock with the greater dip is as distinctly 

 quartz rock as the other, and there is also 

 a large ledge of quartz rock upon the 

 E west side of Lake Champlain with the 

 same inclination. Hence the sudden 



Section across West Haven, vt., and Whitehall, N. Y~ change in the dip is to be regarded as a 



safer distinction between the silurian and 

 Laurentian series, than a difference of lithological character. 



This change of dip is represented in the annexed figure (Fig. 168.) It passes through 

 the south end of West Haven, a mile north of the town of Whitehall, and hence the east 

 part of the section, showing the calciferous sandrock, is in New York. 

 Range, Extent and Thickness. 



There are three different localities in which this formation occurs in Vermont : in 

 West Haven, Orwell, and the east part of Shoreham. In West Haven it may be 

 traced about three miles, from the mouth of Poultney River, to the north, when it 

 either thins out entirely, or passes under the next rock above. It is not seen in New 

 York between Whitehall and Ticonderoga, upon the west side of Lake Champlain : 

 hence, as it appears in Vermont nowhere between West Haven and Mount Inde- 

 pendence, it is probable that it may be found beneath the calciferous sandrock, the 

 whole of this distance about eighteen miles. At Mount Independence it is hardly 

 consequential enough for the map ; as it occupies twenty or thirty feet of altitude at the 

 base of this mountain, and extends about a quarter of a mile north and south, upon 

 the edge of Lake Champlain. From thence it crosses the lake to Ticonderoga, where it 

 is much thicker. 



The Potsdam (?) sandstone in Shoreham is of limited extent. It is less than two 

 miles in length, and an eighth of a mile in width, and it is perhaps thirty or forty 

 feet thick. It was first pointed out by Prof. Emmons. There are no fossils in it to 

 determine its age, but the limestone overlying it is said to have a lower silurian maclurea 

 in it. It must have been elevated to its present position subsequently to its formation, 

 as the first rock west of it belongs to the Hudson River Group. 



The thickness of the Potsdam sandstone at Whitehall is stated by Prof. Mather to be 

 from one hundred and fifty to two hundred feet. It thins out rapidly as it passes north- 

 ward, though not as suddenly as some have stated. There must be about fifty feet of 

 thickness as it enters Vermont ; and to the north it passes beneath the calciferous sand- 

 rock, so that its thickness beneath the latter is not known. Most of this formation in 

 West Haven is concealed by overlying clay. The only mineral in the State Cabinet from 

 this rock is Labradorite. 



Fossils. No organic remains of positive character have been discovered in the Potsdam sandstone in 

 Vermont. The best characterized species of the group, found near by, in New York, are the Scolithus lin- 

 earis (Hall), Lingulaprima (Con.), L.antiqua (Hall), and Conocephalites minutus (Bradley.) 



In Iowa, Prof. Owen has described from the Potsdam sandstone, five species of Dikeloceplialus. 

 18 



