GEOLOGY OF THE LAKE PLACID QUADRANGLE II 



wide, lies 1859 feet above sea level. ^ By many it is regarded as 

 the gem of Adirondack lakes. Mt Whiteface rises majestically 

 more than 3000 feet above the surface of the lake on the north- 

 east, and Moose mountain rises over 2000 feet above the lake on 

 the west. The lake contains two large, high rugged islands and 

 one small one. 



Morgan pond on Wilmington mountain has a remarkable situa- 

 tion at an altitude of 3020 feet. 



The Lake Placid quadrangle contains a wonderful variety of 

 rock formations, including most of the familiar Adirondack types 

 as well as several, others described in this bulletin for the first time. 

 Excepting the Pleistocene deposits, all the rocks are of Precam- 

 brian age. 



Oldest of all is the Grenville series which takes rank among the 

 very oldest rock formations of the earth. It consists of gneisses, 

 quartzites, and cr3'stalline limestones. These are sedimentary rocks 

 which have been thoroughly crystallized. There are no large areas, 

 but many small masses are scattered throughout the quadrangle. 



Next in age, definitely proved, is the Marcy type of anorthosite 

 with its extensively developed facies known as the Whiteface 

 anorthosite. These rocks, which are igneous in origin, are intru- 

 sive into, and therefore younger than, the Grenville rocks. Anor- 

 thosite is the most abundant rock of the quadrangle. 



The syenite-granite series, with its several variations, is intrusive 

 into both the Grenville and the anorthosite. It ranks next to the 

 anorthosite in areal extent. 



Of particular interest is a peculiar rock, called the Keene gneiss, 

 occurring as a border zone between the anorthosite and the syenite- 

 granite. There is strong evidence that this rock has resulted from 

 the assimilation of anorthosite by the molten syenite or granite. 



At several places in the northern portion of the quadrangle there 

 are series of parallel, gneissoid, basic, usually badly weathered 

 dikes cutting the granite. They are different from any rocks 

 hitherto observed by the writer in the Adirondacks. It is probable 

 that they are older than the gabbro below mentioned. 



A number of gabbro bodies of the usual Adirondack kind occur 

 within the quadrangle. These are seen to cut both the Grenville 

 and the syenite-granite series. 



"■ The altitude number 1864 printed on the accompanying map was 

 determined by an older survey. 



I 



