History of the Geology of New York Island. 109 



it did, with the geology of the adjacent mainland and islands, 

 and describing the points of difference. 



The following is an abbreviated description of the Island of 

 New York, from Akerly's Essay : 



" The south part is an alluvia], on a granitical base, which appears at 

 the Battery. The northern part of the Island is of the primitive forma- 

 tion. The body of granitical rock, forming the base of the Island, has 

 a direction nearly between southwest and northeast. It appears to be 

 veined or stratified in that direction, as may be seen where quarries have 

 been opened to procure building stone. Where no disintegration has 

 taken place from decomposition, the color of the rock is bluish or gray- 

 ish blue. 



"The various aggregates found among granite are seen in different 

 parts of this country — as granatines (ternary combinations), granitelles 

 (binary aggregates), granilites (aggregates of more than three compo- 

 nents), gneiss, etc. 



"Rocks, in which magnesian earth predominates, are frequently 

 found, though not in large masses, but mostly in detached pieces. 

 Some of these are steatites, some serpentines, and others asbestus. 

 Many elegant specimens of steatites may be procured, some of which 

 have handsome dendritical appearances upon them. 



" The serpentines are not very beautiful ; but there are a great variety 

 of the forms of asbestus, some of which approach to amianthus. The 

 stellate, the plumose, and the fibrous asbestus, are met with as well as 

 the ligniform. 



" On the northernmost part of the Island of New York, near where 

 it is united to Westchester by Kingsbridge, is the commencement of a 

 limestone formation of the primitive class. It is white and granular, 

 and contains beds and veins of quartz and granite, and is also associated 

 with tremolite. Rubilite, or red schorl, has been found in it; and our 

 associates, the Rev. Frederick C. Shaeffer, and Dr. Peter S. Townsend, 

 have also discovered pyroxene in this limestone. 



"The limestone (says Dr. Bruce) has running through it, in different 

 directions, veins from one to three or four inches thick, composed of 

 quartz, feldspar, and mica, and granular limestone, through which 

 the oxyde of Titanium is sparingly disseminated. 



