QUARRY MATERIALS OF NEW YORK 5 1 



In the Adirondack region no basement or crystalline complex 

 assignable to the Archean period has been discovered. The oldest 

 igneous rocks apparently have intrusive relations with the sediments 

 whenever they come in contact with the latter, and consequently 

 the first recognizable elements are of clastic origin, classed as 

 Grenville or Algonkian. . These consist of crystalline limestones 

 or marbles, banded and foliated gneisses, hornblende and mica 

 schists, and quartzites. They are interfolded with the early igneous 

 gneisses and have been invaded and injected by all the Precambric 

 intrusions. They have consequently a patchy distribution, though 

 forming belts of rather wide extent on the northwestern side. They 

 bear no recognizable life remains and the only evidence that life 

 existed at the time is the abundance of carbon in the form of 

 carbonates and graphite. The more important quarry materials 

 of Grenville age are the limestones which yield building and monu- 

 mental marbles and are sources of high-grade limes. 



The deep-seated igneous rocks consist of granites (both gneissoid 

 and massive), syenite, gabbro and anorthosite. Among the granites 

 may be recognized at least two classes based on their relative age ; 

 an older, much compressed, finely granular variety that has been 

 squeezed out and elongated into beltlike bodies, and a younger, 

 massive, coarser type that occurs in the form of bathyliths and 

 bosses. In the earlier series may be present parts of the Archean 

 basement if they are anywhere existent. The younger granites are 

 most useful for quarry purposes. The Adirondack syenite has 

 sometimes a reddish color, like that of much of the granite into 

 which it grades in places, but the characteristic and by far the 

 most widely developed variety is a green augite syenite, usually 

 with the original textures and structures well preserved. There 

 are, however, crushed and more or less foliated types of the green 

 syenite. The gabbros are found in dikes and bosses as separate 

 intrusions and as border phases of the anorthosite with which there 

 appears to be complete gradation. The anorthosite constitutes an 

 immense bathylith in the east central section of the Adirondacks, 

 the largest intrusion of the whole region and, except for a few 

 areas of Grenville which were probably engulfed during its approach 

 to the surface, a practically unbroken mass. The several periods 

 of igneous activity to which these deep-seated masses may be as- 

 signed were probably times of crustal upheaval and metamorphism, 

 at least the varied conditions of foliation, crushing and recrystalliza- 

 tion which are exhibited by the intrusions seem to be significant 

 of repeated modifications by dynamic agencies. As the last mani- 

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