FOSSILS. " 307 



Bridport, where the usual graptolites of this rock were found. It is interrupted before 

 reaching Chimney Point by Chazy limestone. It is found again at Elm Point in the west 

 part of Addison. To the north, in Addison and in Panton, it contains the characteristic 

 fossils. A loAver limestone in the west part of Panton, again pushes this rock into the lake 

 and it re-appears for the last time in Vermont at Adams' Ferry, in the north-west part of 

 Panton. As before mentioned, it occurs in New York north of Split Rock. 



While it is difficult to draw the line, in all cases, between the Utica slate and the Hud- 

 son River shales in the eastern range of slate, we have never felt any doubt as to the 

 propriety of the name Utica for this band along the shore of the lake. Apart from its 

 fossils, its thickness and extent are so small as to preclude the possibility of the presence 

 of any newer rocks in connection with it. 



The thickness of the Utica slate and Hudson River shales combined, has already been 

 stated. We think that generally the thickness of the former, in Vermont, is about 100 

 feet, as stated by Prof. Adams. In Grand Isle the thickness must be greater, but we 

 have used no means to ascertain how much greater it may be. 



MINERAL CONTENTS. 



The veins of milk-white and nearly transparent calcite have already been mentioned. So have 

 the nodules of pyrites, which are extremely abundant in the North and South Hero Islands. Several 

 mineral springs occur in this formation. The one at Alburgh is the best known. It is strongly 

 impregnated with sulphureted hydrogen, and is visited by many invalids with beneficial results. It is in 

 the east part of the town. We visited a similar spring, impregnated with the same reagent, near the 

 church in South Hero, upon the land of Abel Phelps. Its quality is good, but we cannot compare it with 

 the former spring, as we have not tested the qualities of the Alburgh water. It is probable that the sulphur 

 arises from the decomposition of the nodular pyrites common in the slate; and that many similar springs 

 of good quality may be found in this formation elsewhere. 



FOSSILS. 



Several species of fossils have been found in this rock in the limits of Vermont. They are Graptolithus 

 pristis (Hisinger), G. bicornis (Hall), Crania (?) filosa (Hall), and Triarthrus Beckii (Green.) 



Graptolithus pristis (Hisinger). Linear, straight, scarcely a line broad, compressed; rachis central, cap- 

 illary; both sides with broad acute teeth. 



This species occurs in small, short fragments, sometimes nearly two inches long. When the specimens 

 are flattened, a central capillary axis is very perceptible, extending the entire length. In some specimens 

 where the serrated portion is removed, this central axis is still preserved, extending beyond the 

 other parts of the fossil. It expands gradually, from what appears to be the base upwards for 

 some distance, but rarely exceeds a single line in width. The serrations are usually acute, but 

 sometimes obtuse. 



Fig. 223 represents a fragment of the Graptolithus pristis from the Utica slate. This species 

 has been found at several places on the shore of Lake Champlain in Bridport, along the same 

 shore in some parts of Addison, at Snake Mountain, in Addison, at Adam's Ferry, in Panton, in 

 Grand Isle, and at numerous localities upon North Hero; particularly upon its west side. Gr p?i?ili! 1 "* 



G. bicornis (Hall). Stipe linear, elongated, compressed, narrow, gradually widening from the 

 base upwards; width one line or less; serrated on both sides; serratures slightly oblique; teeth about half the 

 width of the stipe, obtuse at the extremities; axis capillary; base or radix bifurcate. 



This species is easily identified bv the obtuse teeth which are separated from each other by a narrow slit, 



