62 BULLETIN OF THE 



reddish brown and greenish serpentine, traversed by a fine netwoi'k of 

 dolouutic veins. The microscopic characters of the decomposed perido- 

 tite were given to some extent -by Dr. Wichmann, who, it would seem, 

 had onlv the serpentine, under which name he describes the rock.* 



The geological history of this rock is very interesting. Dr. Houghton 

 thought that it was an eruptive rock, and younger than the sandstone 

 ■which was uplifted by it, believing it to be a greenstone impregnated 

 with serpentine. He states that, near the line of junction, the sedi- 

 mentary rock has been greatly shattered, and its fissures filled with 

 injections of calcareous matter. Dr. John Locke thought the "light 

 green trap " was interfused with the sandstone at this point. 



Messrs Foster and Whitney considered that the rock was an immense 

 consolidated lava flow, although it wanted the vesicular structure, while 

 the part filled with the white veins was regarded es a volcanic sand or 

 ash deposited on the lava stream. Younger than this azoic lava was the 

 sandstone deposited upon it (Potsdam). Chemical analysis was given of 

 it, but no name assigned to the rock. Later, this was regarded as 

 closely related to serpentine by Professor Whitney, who gave three 

 'analyses of it.f Later, Dr. Hunt, accepting Professor Whitney's analy- 

 ses, regarded this rock as a somewhat impure sedimentary serpentine 

 belonging to the Huronian series. 



Dr. Rominger later regarded this rock as a half-decomposed basalt or 

 highly ferruginous serpentine ; the part filled with the veins was taken 

 to be an older sedimentary rock, a dolomite, npheaved and broken by 

 the trap, and overlaid by the conglomerate and sandstone. This sand- 

 stone is supposed to have been deposited in the inequalities of the 

 underlying rock following its contours. He thought it most probable 

 that the sandstone was deposited at its present inclination, although it 

 may have been slightly upheaved since. The conglomerate beds at the 

 base of the sandstone are said to contain numerous fragments of the un- 

 derlying rock, We regard this peridotite as an eruptive rock, younger 

 than the sandstone overlying it, and agree in this particular with Dr. 

 Houghton. The portion filled with veins, that was taken by him as 

 a sedimentary rock belonging to the sandstone, or a mixture of sand- 

 stone and trap ; as a volcanic sand or ash, by Messrs. Foster and Whit- 

 ney ; and as a dolomite, older than both the trap and sandstone, by Dr. 

 Rominger, — we regard as simply the upper portion of the intrusive mass 

 modified by its contact while heated with the overlying sandstone, and 

 by the percolating waters since. 



* Geol. of Wise, III. 619. t Am. Jour. Sci., 1859, (2,) XXYIII. 18. 



