QUARRY MATERIALS OF NEW YORK 145 



latter arc almost identical in mineral composition with the diabase 

 trap. Like these they are very tough resistant rocks,, but normally 

 are coarser grained and consequently would not wear so evenly 

 under abrasive conditions. The gabbros occur in dikes, larger than 

 those in which the diabase is found, but more frequently they form 

 rounded and irregular masses or stocks from a few hundred square 

 feet to several acres and even miles in area. They are very common 

 in Essex county within the Lake Champlain drainage area where 

 their occurrence in part is well shown on the Elizabethtown-Port 

 Henry geologic sheet. 1 



The texture of the gabbros and syenites varies from coarse to 

 fine, the finer sorts being on the borders of the areas, where the 

 magmas were subject to quick chill. In these border places are to 

 be found the most suitable material for crushed stone. Some of 

 the gabbros exhibit textures very similar to the trap, their feldspar 

 being in lath-shaped crystals which form a network that incloses 

 the pyroxene in the meshes. Such border phases are practically 

 equivalent to the diabases and should prove equally serviceable 

 as materials for crushed stone of the best quality. 



Numerous chemical analyses of the Adirondack traps, gabbros 

 and syenites have been published in the geologic reports of this 

 region. 2 



LITTLE FALLS, HERKIMER COUNTY 



An outlier of the Adirondack crystalline rocks occurs in the 

 Mohawk valley at Little Falls where quarries for the supply of 

 crushed stone and, to a smaller extent, of building material have 

 been operated for many years. The situation is very advantageous 

 for extraction and marketing of stone as the area is crossed by 

 two main railroad lines and the Erie canal, and there are bare rock 

 ledges close at hand which afford good quarry sites. The rocks 

 are principally adapted for road, concrete and foundation work, 

 being rather dark for use in buildings. They include a fine-grained 

 syenite which occupies most of the area, reddish granite and trap, 

 the last occurring in a dike over ioo feet wide — the largest known 

 in the southern Adirondacks. 



The Little Falls outlier has been mapped and described by H. P. 

 Cushing in connection with his report on the " Geology of the Little 

 Falls Quadrangle " (N. Y. State Museum Bulletin Jj). It consists 

 of a single area of these Precambric crystallines that outcrops within 



1 Included in N. Y. State Mus. Bui. 138. 



2 See especially Museum bulletins 95 and 138. 



