HISTORY OF GEOLOGICAL SURVEY. 3 1 



of the rocky masses, by careful induction. The whole party were ani- 

 mated with the desire to accomplish this object, and therefore visited 

 the almost inaccessible peaks and ravines, one after another, till all had 

 been explored. The actual exertion often put forth for procuring a single 

 specimen was greater than to pass over Mt. Washington on foot, by the 

 paths. Its location may have been three or four thousand feet above the 

 camp, and the country to be travelled was the original forest, never before 

 traversed except by hunters, full of underbrush, fallen trees, and at the 

 higher elevations consisting of the stiff dwarf spruces, through which trav- 

 elling is almost impossible. After overcoming the difficulties of threading 

 the forest and ascending the precipices, the rarified air of the upper re- 

 gions has made even slight exertions burdensome. We take great pleas- 

 ure, therefore, in pointing to the results of our labors, as they have been 

 acquired only through infinite toil ; and we feel sure that if our generali- 

 zations are not accepted, it will be a long time before any other party will 

 labor so hard as we have done to disprove our theories. 



A sketch of the various opinions that have been entertained respecting 

 the age and structure of the White Mountains was presented at some 

 length in the report for 1870; also, further definitions respecting the Coos 

 group, and the manner in which the valley of the White Mountain notch 

 had been excavated. The conclusions expressed concerning the strati- 

 graphical structure have not been modified by subsequent explorations. 

 The following opinion is expressed as to the age of the series : 



In fine, the White Mountain rocks are believed to belong to two great 

 systems, the Gneissic and the Coos group. The first are, for convenience, 

 called the White Mountain series ; and in the area of the model are vari- 

 ous imperfect gneisses, verging into mica schists, a few beds of genuine 

 gneiss, granitic gneiss, andalusite gneiss and granite, both bedded and in 

 veins. These rocks appear to underlie the Coos group, and are therefore 

 older. The presumption is that they are entirely Eozoic, though it is not 

 clear whether they are to be considered as the equivalent of the Lauren- 

 tian of Canada, or more nearly the age of the Cambrian of Great Britain, 

 as restricted by the government survey. 



This White Mountain series has a great development in the middle and 

 southern parts of the state, perhaps embracing everything not included in 

 the Exeter, Merrimack, and Coos groups. Its satisfactory reference to 



