No. 104.] 191 



while the true compact gneiss is seen at the quarries in Saratoga 

 county, and the partial or entire absence of the mica characterizes the 

 rock at many localities farther to the north. This gray gneissoid 

 rock graduates downward, through alternating beds of variable 

 character, into a hornblende rock, and becomes a compact dark- 

 colored sienite extremely hard and tough in its character. 



The same general features prevail in the granite rocks in the 

 Highlands as exposed along the Hudson river, the strata being tilted 

 at a high angle. In many places, however, the lines of bedding 

 become obscure, the mica is to a great degree absent, and the rock 

 assumes the character of a true granite. The principal points of 

 exposure, where the gneiss or granite of the Highlands has been 

 quarried, are at Butter hill, on the west side of the river, and at 

 Breakneck on the east side. In some portions of the mass, at both 

 of these localities, the rock loses in a measure its gneissoid character, 

 and presents a comparatively even admixture of the component 

 parts. At both localities the rock is penetrated by trap dykes, 

 which have affected the beds adjacent to them ; and these, together 

 with other causes, have produced a more than ordinarily fractured 

 or jointed condition of the rock. 



In the higher part of the Laurentian series, and in localities more 

 inaccessible to means of transportation, we have the highly felspathic 

 granites of tiie central portion of the Adirondack region. These are 

 usually coarsely crystalline and of a dark color, but weathering to a 

 lighter hue. They have nowhere been brought into use for building 

 purposes ; and not being within the limits of reasonable cost of 

 transportation, it is scarcely worth while to indicate their localities 

 more particularly. 



Gkanites of New England. 



The granites examined beyond the limits of the State belong to 

 an entirely different geological age from those of New York, and 

 present a different aspect in the aggregation of their component 

 parts. They moreover differ among themselves, in a very extrenie 

 degree, both in color and texture ; varying from the dark-colored 

 compact sienite of Quincy and the neighborhood, through the lighter- 

 colored varieties of the same locality and that of Chelmsford and 

 other places, to the greyish-white varieties like that of Rockport on 

 Cape Ann. All the quarries that I have examined along the coast 

 are free from mica ; and when hornblende is not present, we have 

 the quartz and felspar only. The dark colors are usually due to the 

 presence of hornblende ; the reddish or brownish colors, to the 

 colored felspar ; and some of the quarries offer a granite of quartz, 

 brownish felspar and dark hornblende, giving thus within these 

 ranges a considerable variety of color, due either to the original 

 color of the substances, or to the proportions in which they are 

 mingled in the mass. 



The principal quarries that came under my observation were those 

 of Quincy and Weymouth, Rockport on Cape Ann and Dix island 



