July 20, 1900.] 



SCIENCE. 



87 



titanites scattered through the aggregate. 

 It seems to be a metamorphic product from 

 the transition sediments between the lime- 

 stones and the associated elastics. 



Likewise associated with the limestones 

 in several localities, but more especially at 

 Port Henry and Fort Ann, there are horn- 

 blende schists, of dark black color. They 

 are often involved with the former in a 

 most intricate way, running in as tongues 

 and stringers, penetrating as dikes, which 

 may be broken up into several scattered 

 masses, or appearing as single boulder-like 

 inclusions. In all cases where the rocks 

 are prominently developed, there is easily 

 recognized, intrusive gabbro in the vicinity 

 and the burden of probability would seem 

 to favor an igneous origin for them. At 

 the same time calcareous, magnesian shales 

 might be responsible for similar mineral 

 aggregates, when exposed to excessive meta- 

 morphism, as Professor Emerson has shown 

 for the Chester region of central Massachu- 

 setts, and in localities of compression and 

 mashing they might become involved in a 

 complex way with softer beds such as lime- 

 stones ; but still I think the Adirondack 

 evidence favors irruptive contacts for them 

 and the mashing and involution of dikes. 



An almost invariable associate of the lime- 

 stones, but in comparatively small amount 

 is a rock consisting of a granular aggregate 

 of dark green pyroxene. Some little calcite 

 may often be detected in the interstices be- 

 tween the pyroxene, but as a rule the 

 coarsely crystalline bits of the former make 

 up practically the entire mass. The rock 

 has manifestly resulted from the metamor- 

 phism of siliceous transition deposits from 

 the limestones to the elastics. 



Garnet Pyroxene Rooh. — At two localities, 

 one in Keene valley, on the west bank of 

 the Ausable river and about a mile above 

 Keene Center, and the other in northwest- 

 ern Lewis, extensive ledges of a peculiar 

 rock have been met that seems to belong to 



the limestone series. It is quite massive 

 and gives no trace of dip or strike. It is a 

 coarsely crystalline aggregate of deep red 

 garnet, and green monoclinic pyroxene. In 

 each case the ledges are associated with 

 hornblendic gneisses and they may be a 

 peculiarly altered, calcareous sediment, but 

 the mineralogy strongly suggests contact 

 metamorphism upon limestones, although 

 in neither case was it possible to establish 

 the presence of eruptives in the immediate 

 vicinity. In the Keene locality anortho- 

 sites are in masses of mountain size, within 

 half a mile, but gneisses intervene. In the 

 latter case no eruptives of the gabbro family 

 are near enough to be reasonably consid- 

 ered causes in the effect. 



The Sedimentary Gneisses. — In intimate re- 

 lations with the limestones in many locali- 

 ties and in quite extended outcrops, without 

 them in other places, are gneissoid rocks 

 that are quite certainly altered sediments. 

 They are characterized by a very pro- 

 nounced and persistent banding and the 

 banding is regular and runs for very con- 

 siderable distances. The transitions from 

 dark bands, consisting of prevailing bisili- 

 cates to lighter ones containing quartz and 

 feldspar are abrupt and can only be ac- 

 counted for by changes in sedimentation. 

 They differ entirely from the short lenticles 

 which are produced by the stretching of the 

 minerals of an eruptive rock. The layers 

 are at times quite pure quartz and again 

 suggest the mineralogy of pegmatites. 

 Graphite is a very common mineral and is 

 one of much significance. 



On account of fragmentary exposures and 

 the ever present drift or forest growth it is 

 difficult to determine the actual thickness 

 of these rocks. In southwestern Jay town- 

 ship, Essex county, I have paced carefully 

 over a series of continuous exposures of 

 very regular and flat dipping beds that 

 were at least 75 feet thick and then 

 became concealed under drift. A mile 



