GEOLOGY OF MOUNT MARCY . 1/ 



dence, however, did not appear. One goes from one rock to the 

 other across small valleys or gulches with fault escarpments. The 

 same types of rock are involved in the most intimate way in the 

 pass traversed by the old highway, northwest of Pitchoif mountain. 

 They have been interpreted as syenites and are described as such 

 under the syenites where the mineralogy is further discussed. A 

 candid observer can not, however, disguise from himself the pos- 

 sibility that old Grenville shales may, under extreme metamorphism, 

 assume a mineralogical composition not appreciably different from 

 the acidic phases of the syenite series. 



The basic, homblendic phases of the Grenville are less prominent 

 in the small areas of the Mount Marcy quadrangle than in the 

 larger exposures of the Elizabethtown and Port Henry quadrangles 

 already described in Museum Bulletin 138. Shaly limestones or 

 extremely calcareous and more or less ferruginous shales could 

 yield aggregates of hornblende, orthoclase, plagioclase, biotite and 

 magnetite. The hornblendic rocks might also conceivably be tongues 

 of intrusive basic syenite, crushed and sheared in the dynamic pro- 

 cesses through which the area has passed. The peculiar green and 

 doubtless soda-bearing pyroxene of the syenites would be a very 

 peculiar and unusual mineral in metamorphosed sediments. 



Contact zones. The best contact zones thus far discovered in 

 the eastern Adirondacks appear in the northern edge of the quad- 

 rangle. While they vary somewhat among themselves they do 

 present in one exposure and another very typical cases of these 

 phenomena and some interesting variations on the general theme. 

 They may be taken up from the simplest cases to the most complex. 



Cascadeville. Many years ago early observers noted that in the 

 talus at the foot of the mountain southeast of the barrier between 

 the two Cascade lakes, then known as Long pond, there appeared 

 specimens of green diopside and associated minerals in bluish calcite. 

 The fallen blocks can be easily traced to the parent ledge higher 

 up on the mountainside. The simplest explanation of the relations 

 of this limestone seems to be the following : It is a mass of Gren- 

 ville limestone included in the anorthosite which constitutes Cascade 

 mountain. 



The exposure of limestone at the Cascade lakes was well known 

 to Prof. Ebenezer Emmons during his work on the second district 

 of the State from 1835 to 1840. On pages 228, 229 of his valuable 

 and interesting report he speaks of it as follows : 



Passing now to the northwest part of the county we find several beds of 

 primitive limestone, under nearly the same conditions as in the southern 

 and eastern parts. Long pond is one of the most interesting; it is in the 



