July 20, 1900.] 



SCIENCE. 



85 



of the exposures, it will be well to give a brief 

 resume of the kinds of rocks with which we 

 have especially to deal. Right in this par- 

 ticular appears the great difficulty of a 

 metamorphic problem. In sedimentary or 

 unaltered igneous rocks we are never at a 

 loss to understand their nature and method 

 of origin, but in excessively metamorphosed 

 varieties the great difficulties arise in de- 

 scribing these questions at the very outset, 

 and if we were only sure of many of these 

 puzzling gneisses, the battle would be more 

 than half won. 



The Limestones. — The most easily recog- 

 nized is a coarsely crystallized, white lime- 

 stone and it is at the same time the widest 

 in occurrence and the most significant evi- 

 dence of the presence of the old sediments. 

 While at times of considerable purity, as 

 at the marble quarries at Gouverneur, it is 

 generally more or less richly impregnated 

 with graphite, apatite, quartz, pyroxene, 

 horneblende, phlogopite, biotite, scapolite, 

 chondrodite, ga,rnet and feldspars. The 

 silicates tend to be aggregated into streaks 

 and bunches, that owe their shape in large 

 part to the shearing and stretching effects 

 of dynamic metamorphism. In the larger 

 bunches, less common minerals, such as 

 titanite, pyrrhotite and tourmaline are met. 

 Most of the minerals cited above are 

 without doubt produced by the regional 

 metamorphism of more or less siliceous 

 limestones. Such are quartz, pyroxene, 

 hornblende, biotite, graphite, apatite and 

 feldspar. But others, such as tourmaline, 

 chondrodite, scapolite, titanite and to some 

 degree apatite are the results of contact 

 metamorphism, as Smyth has so well shown 

 for the west side of the area. 



A variation which is met in several lo- 

 calities, appears when the marbles become 

 charged with serpentinous alteration pro- 

 ducts, from pyroxenic originals ? This is 

 true, most prominently, in Moriah town- 

 ship, Essex county ; and in Thurman town- 



ship, Warren county, although the same 

 rock is met in less amount in a number of 

 other places. 



Regarding the development of these 

 limestones it may be only said here, that 

 they are beyond question calcareous and 

 magnesian sediments which involved sili- 

 ceous, ferruginous and aluminous admix- 

 tures, in some cases very richly. During 

 metamorphism the latter elements supplied 

 the materials necessary for the production 

 of various silicates. The limestones appear 

 to be less pure and consequently more 

 charged with silicates on the east than on 

 the west, and to present smaller cross-sec- 

 tions, but from this statement we must 

 omit the contact zones of St. Lawrence 

 county. In judging of the impurity of the 

 limestones we must also make exception of 

 the included masses of rocks, composed of 

 silicates, which in the dynamic metamor- 

 phism, have been torn off from the wall 

 rocks or from pegmatite or more basic dikes 

 that had penetrated the limestones before 

 the disturbances. I also reserve graphite 

 for special consideration further on. The 

 limestones exhibit many interesting proofs 

 of having yielded to pressure like viscous 

 substance. They have flowed around the 

 harder inclusions and bordering rocks, have 

 moulded themselves into their irregulari- 

 ties, and have behaved in all respects like 

 a plastic material. This property on their 

 part has made the determination of accu- 

 rate dips and strikes a matter of difficulty 

 and has added to the obscurity of the prob- 

 lem. 



The Quartzites. — But little has yet been 

 stated in print regarding the rocks of this 

 type and they are indeed far less abundant 

 than the limestones. In former papers 

 reference has been made to thin sulphur- 

 yellow beds which accompany the lime- 

 stones near Port Henry. They are friable 

 quartzites and contain much sillimanite, 

 graphite and pyrite. At Hague, a town on 



