212 TRANSACTIONS OF THE [APR. 24 



of mica and the large amount of recrjstallization, is due the 

 lack of foliation. That the garnet has been formed at the 

 expense of biotite originally present is not improbable. 



The contact of granite with crystalline limestone has j)ro- 

 duced some noticeable changes in the latter. Most apparent is 

 a whitening of the rock, with an increase in the coarseness of 

 grain. At the same time scales of graphite and mica become 

 larger and more abundant, while knotty masses of silicates 

 develop to a considerable extent. Microscopic examination of 

 these shows the presence of biotite, muscovite, tremolite and a 

 colorless pyroxene. These minerals are crowded together in 

 such a way that there is no opportunity for the development of 

 crystal boundaries. Similar lumps of silicates are by no means 

 wanting in the limestone at a distance from the granite, but 

 near the latter rock they have developed in unusual abundance. 

 On the whole the contact phenomena are not very marked, and 

 some of the minerals most common in granite- limestone contacts 

 are absent. 



CRYSTALLINE LIMESTONE. 



The limestone is, on the whole, quite uniform in composition 

 and structure, though variations from the normal type pro- 

 duced by the presence of diflerent minerals, are common. The 

 normal rock is coarsely crystalline, varies from white to dark 

 gray, and contains abundant mica and graphite. Weathering 

 gives a darker color to the surface, while the cleavage faces be- 

 come roughened by parallel ridges, due to solution along basal 

 twinning planes. 



Pyroxenic phases of the limestone are quite common. The 

 pyroxene is, as a rule, colorless, and has a high extinction angle. 

 It seldom shows distinct crystal outline, being in irregular 

 grains of small size. Tremolite is also found, occurring in a 

 similar way, but seemingly less abundant than pyroxene. 

 Probably genetically connected with these phases of the lime- 

 stone is the serpentineous variety, though the connection has 

 not been absolutely proved. The serpentine forms rounded 

 grains in the rock, sometimes equalling the calcite in quantity. 

 Merrill * has shown for similar rocks in Wai*ren County that 

 the serpentine is derived from joyroxene. In the present in- 

 stance no serpentine has been found containing a core of pyrox- 

 ene ; but its structure is often such as would result from its 

 derivation from pyroxene, or from hornblende, and as these 



* Merrill. G. P. On the Opbiolitc of Thurman. Warren Co., N, Y-. with 

 remarjis on the Eozoou Canadenae; Aui. Jour. Sci- III., XXXVII, p. 18'J. 



