HISTORY OF GEOLOGICAL SURVEY. 



57 



granites and felsites together constitute a great series of formations, 

 which, I suppose, are the equivalents of the Labrador system of Logan. 

 He has not given the Hmits of his system ; but I retain the name sug- 

 gested by him for the group of granites and compact feldspars developed 

 so finely in New Hampshire. There is an extensive mass of granite in 

 Wolfeborough and New Durham, which may be connected with the 

 Labrador system, but its relations have not yet been made out with 

 certainty. 



7. Eruption of Sienite. The Belknap Mountains, certain peaks in 

 Alton, Diamond island, and probably Rattlesnake island in Winnipiseogee 

 lake, and Red hill in Moultonborough and Sandwich, are composed of 

 sienite of various textures, which seems to have been erupted after the 

 deposition of the felsites. Its age is shown by the fact that it cuts the 

 ossipyte in Waterville. 



8. Deposition of Mica Schists. This formation is enormously devel- 

 oped in Strafford and Rockingham counties, touching the lake only at 

 Alton Bay. It evidently covers all the formations thus far specified. 



This is the last of the solid rocks in this area. There succeeds an 

 enormous interval of time, of which we have no record in New Hamp- 

 shire. The country must have been elevated, so that no deposits could 

 be formed. The intei-val embraces the principal portion of the fossil- 

 iferous rocks. 



g. Glacier Period. The phenomena of this age about the lake are 

 striae, embossed ledges, pot-holes, beds of clay, boulder drift, etc. The 

 courses of the striae usually agree with that of the valley, or from 

 S. 2S°-30°E. 



10. The Terrace Period. The presence of the ocean after the glacial 

 period over the lake may possibly be indicated by the existence of the 

 smelts in its waters, which are marine animals, possibly left behind when 

 the salt water disappeared. The terraces seem to indicate that the water 

 has stood successively at the heights of 100, 80, 55, 30, 23, 15, and 12 

 feet, but never any higher. There may have been egress for the waters 

 in the direction of Squam lake, Gilford, and Alton. 



Lengthy considerations are presented to show, by contrast to these 

 small lake terraces, the fluviatile origin of the large banks of sand and 

 gravel along the Merrimack river valley. The conclusions are of consid- 

 VOL. I. 8 



