530 



PHYSICAL GEOGKAPHY. 



granites and felsites in the former is satisfactorily worked out. The 

 Chocorua rock is essentially a crystalline labradorite. Now this is a 

 mineral usually regarded as very ancient. Whatever it overlies must 

 therefore be older. Hence the Montalban rocks are more ancient than 

 the Chocorua granite in New Hampshire ; and, as we find the same 

 formations near Rutland, and grouped in the same way, it is fair to infer 

 that they belong to the same series as those in New Hampshire. There- 

 fore we have a new argument for the Eozoic age of the Green Mountain 

 range. I wait only for the results of certain chemical analyses to publish 

 the details of this discovery, and its bearing upon the age of the Ver- 

 mont formations. 



Fig. 6l.— SQUAM LAKE AND MT. CHOCORUA. 



Several of the Labrador areas upon the map represent an important 

 eruption of sienite after the deposition of all the members which have 

 now been specified. Such are the elliptical area in Moultonborough 

 and Sandwich, or Red hill ; part of the Waterville patch, consisting of 

 Mt. Tripyramid ; the long strip from Dover to Salem ; the northern end 

 of the large expanse of this rock in Massachusetts; Mt. Monadnock, 

 opposite Colebrook, etc. Up Norway brook in Waterville this rock has 



