334 Prof. Beck on Igneous Action, as exhibited in Neio York. 



well defined. They usually have a slaggy aspect, their angles 

 being obliterated, and their surfaces covered with a kind of glaze; 

 while not unfrequently groups of crystals have coalesced into one 

 mass or united together like the glass beads found among the 

 ruins of the great fire in the city of New York, (1835.) These 

 remarks will apply also to some of the other minerals associated 

 with the scapolite, but the change is rarely so marked. 



Facts similar to the above have been observed in Orange Coun- 

 ty, where the white limestone is frequently in beds in granite and 

 gneiss. In the vicinity of Edenville the apatite found in this 

 rock, often has the bent form and glazed appearance so charac- 

 teristic of this mineral in St. Lawrence County ; and at Amity the 

 so called idocrase, has sometimes two or three perfect faces, while 

 other parts of the crystal look as if they had been softened by 

 heat, and in this softened state had accommodated themselves to 

 the little cavities and fissures of the limestone. 



It may here be remarked, that I have not hitherto observed any 

 appearances like those above described in the dolomitic limestones 

 of the southern part of New York. It is true the pseudomorphic 

 forms of hornblende and pyroxene which I noticed in a for- 

 mer paper are very abundant ; and these it will be observed, I 

 have proposed to refer to an agency similar to that which seems 

 to have produced the peculiarities exhibited in the minerals of the 

 white limestones. It should be borne in mind, however, that for 

 some reason or other, there is a greater poverty of minerals in the 

 dolomites than in the latter rocks. In the former, the different 

 varieties of hornblende and pyroxene are almost the only species, 

 if we except those found in a few metallic veins, some scales of 

 mica, and thin layers of jasper or hornstone. On the other hand, 

 the white limestones abound in spinelle, chondrodite, crystallized 

 mica, feldspar, tourmaline, apatite, scapolite, sphene, graphite, 

 hornblende, pyroxene, and several others which it is not neces- 

 sary to enumerate. 



I proceed now to notice some peculiarities of the minerals found 

 in gneiss and mica slate. The occurrence of crystallized garnets 

 in these rocks has been adverted to by Mr. J. Phillips, as an evi- 

 dence that the whole mass has been subjected to a pervading 

 high temperature. " The occurrence of garnets," he adds, " in 

 mica schist and gneiss is entirely unconnected with any local 

 effect of heat, derived from particular masses of granite, green- 



