304 BULLETIN" 109, UNITED STATES NATIONAL MUSEUM. 



Fitting these to the trigonometric stations obtained as explained, a 

 very accurate map was prepared. The elevations v\'ere obtained 

 chiefly by leveling along the railroads. Rarely, use was made of the 

 railroad survey data. The hills were determined by aneroid and 

 mercurial barometers and estimates. Guyot's measurements for tlie 

 higher mountains were accepted as correct. Leveling from the sea to 

 two stations of the United States Coast Survej'' enabled certain cor- 

 rections to be made. Contours on the maps were 100 feet apart, save 

 in the extreme north and south, where they were often given for every 

 50 feet. 



The parallel linear arrangement of the formations allowed the 

 measurement of 13 sections from east to west across the State. Every 

 ledge along these lines was examined and specimens collected of every- 

 thing important. These were subsequently arranged in the museum, 

 as noted later. 



Tavo fields, each 400 to 500 square miles in extent, were studied with 

 unusual care — one the Ammonoosuc mining field and the other the 

 White Mountains. Every ledge in these districts was visited and 

 special collections made for the museum. 



An extraordinary number of observations, it is claimed, were taken 

 of the surface geolog}^, and the survey was the first to give prominent 

 attention to the subject of micropetrology. This work was in the 

 hands of Dr. George W. Hawes. 



The several methods employed by the survey, and which v/ere 

 original with it, were as follows: 



1. Determining topography by careful surveys of the ridges of 

 land or watersheds and river courses and filling in subsequently the 

 rest of the field by estimate. 



2. Methods of studying surface geology. 



3. Microscopic methods in lithology. 



As already noted, the survey collections were assigned to the New 

 Hampshire College of Agriculture, located in a building belonging 

 to Dartmouth College. This museum consists of («) rocks illus- 

 trating sections; (h) rocks illustrating ledges between the section 

 lines, about 500 localities being represented; (<?) special collections, 

 much more minute, as of the White Mountains, Ammonoosuc mining- 

 field, Helderberg region near Bernardston, Massachusetts, and a 

 large collection of rocks to illustrate the dispersal of fragments by 

 ice, also a lithological series; (d) fossils of Niagara age, full repre- 

 sentations of all stones valuable for economic purposes, also a system- 

 atic collection of ninety-five mineral species found in the State, with 

 slides for microscope. Duplicate sets of the first section collection 

 were placed in the State Normal School and in the American Museum 

 of Natural History in New York. To the last named were added the 



