7S2 STUDIES FOR STUDENTS 



rocks, is an accurate base map of sufficiently large scale. Unless 

 the relief is slight or the topography of a simple character, it is 

 essential that the topography be represented either by hachures 

 or contours, preferably the latter. A scale of an inch to the 

 mile (i : 62, 500) with a contour 'interval of twenty feet will no 

 more than suffice to express the detail that is necessary for the 

 best results. If roads are numerous and reasonably good, a 

 bicycle with cyclometer attachment will be a valuable adjunct, 

 and with little doubt the best way of securing base locations as 

 well as getting quickly from place to place. 1 



By the use of the aneroid and 4-inch sighting compass, and 

 by pacing, all locations can probably be made with sufficient 

 accuracy if the base map is reasonably good and the country is 

 one of diversified topography. In a wilderness like that about 

 Lake Superior, where the monotonous uniformity of the topog- 

 raphy and the forest cover make outlook impossible, the matter 

 of location becomes exceedingly difficult. The problem has 

 there been solved by scouring the country for outcrops in parallel 

 and contiguous belts, a compassman accompanying each geologist 

 to keep the direction and pace the distance, so as to allow him 

 some freedom of movement. 



Examination of rock and collection of specimens. - — The exami- 

 nation of the rock is made upon the ground after securing the 

 freshly broken surface of a specimen as little weathered as pos- 

 sible. 



The specimen should be examined with the naked eye for its 

 general aspect and compared with the weathered surface of the 

 outcrop. Its manner of fracturing under the hammer may be 

 of much significance, and of two closely similar rocks it may 

 even remain the chief distinguishing difference in the field 

 observation. With a pocket lens of a magnification of 6-14 

 diameters, according to personal preference, 2 a more careful 

 examination is made of the fresh surface to note the essential 

 and accessory minerals and their relative proportions, the texture 



1 Hobbs, "The Geologist Awheel," Pop. Sci. Month. , Vol. LVIII, pp. 515-518. 



2 The best lenses for the purpose are the Hastings aplanatic triplets, manufactured 

 by Bausch & Lomb, Rochester, N. Y. 



