QUARRY MATERIALS OF NEW YORK 91 



In their typical development the anorthosites are too coarse in 

 texture and too dark in color to find favor as building materials. 

 Much of the interior part of the area is made up of this very coarse 

 type. Along the borders they are usually finely textured owing to 

 secondary crushing, and their color then becomes lighter if not 

 influenced by an abnormal proportion of iron-bearing minerals. 

 Some variations of this border phase present a uniform, even 

 granular appearance, closely resembling in mass a true granite with 

 which the anorthosite compares favorably as regards durability and 

 strength. 



Few quarries have been opened in the anorthosite and these are 

 situated in the northeastern part which is most accessible to the 

 lake. Old quarry sites exist on Splitrock mountain between West- 

 port and Essex village and near Keeseville. Some work has been 

 done, also, on the small outlier in Beekmantown and Altona town- 

 ships, Clinton county. More recently attention has been given to 

 the locality near Ausable Forks, where there is an area underlain 

 by uniform light-colored anorthosite. 



The syenites and granites of this section are found in smaller in- 

 trusions in the midst of gneisses which surround the anorthosite. 

 Both classes show a tendency toward laminated structures and on 

 that account have limited quarry possibilities. The syenite is dark 

 green, while the granite is mostly a red variety. A local develop- 

 ment of massive syenite that occurs at Ausable Forks on the border 

 of the anorthosite, has recently come into prominence as a source 

 of monumental stone. The red granite has been quarried only to 

 a small extent. 



The gabbros have little importance economically except as possible 

 sources of supply of road metal for which the massive types would 

 appear to be excellently adapted by reason of their usually tough, 

 firm nature. They form small intrusive knobs in the gneisses and 

 also are found quite commonly in the anorthosite area. 



In this connection mention may be made of the diabase dikes 

 which occur all over the region, and are particularly abundant in 

 southern Clinton county. Like the other igneous rocks that have 

 been mentioned they are of Precambric age, though they show no 

 effects of pressure metamorphism and must have been intruded in 

 very late Precambric time. They seldom attain a workable size, 

 the average thickness being not more than 10 or 15 feet. For 

 road-making they offer the best material to be had anywhere, but 

 so far no very accessible dikes of large size have been found. 



