PEEVIOUS WORK. 13 



J. L. Ridgway, by whom the colored plates of natural size specimens were 

 prepared. 



PREVIOUS WORK IIST THE DISTRICT. 



On account of its comparatively slight economic importance, and also 

 on accoimt of its isolation, very little work of which the results have been 

 published was done in this district prior to that on which this monograph is 

 based. As a rule, the earlier observers began the season's work either in 

 the Marquette or in the Menominee range, and working westward the 

 Crystal Falls district was reached only as the season neared its close, or as 

 the appropriation was nearly exhausted. The published work upon this 

 district is ffiven below in chronological order. 



Burt, Wm. A. Report of linear surveys with reference to mines and minerals, 

 in the Northern Peninsula of Michigan in the years 1845 and 1846. Dated March 20, 

 1847. Thirty-fli'st Congress, first session, 1850; Senate documents, Vol. Ill, No. 1, 

 pp. 842-882, with map. 



During the year 1846 a linear survey was made of that part of the 

 Upper Peninsula of Michigan described as being bounded on the north by 

 the fifth correction line, on the south by the fourth correction line and the 

 Brule River, on the east by ranges 23 and 26 W., and on the west by 

 range 37 W. This includes in its limits the district under discussion. In 

 the course of the survey, geological observations were made by William A. 

 Burt, the deputy surveyor in charge of the work. The report and accom- 

 panying geological map embodying the results of these observations are 

 concealed among the Senate documents of the Thirty-first Congress. The 

 following quotations from this report give all the observations on the part 

 of the territory surveyed in which we are at present interested: 



Topography. — Wcst of raugs 31 west, and north of the Brule River to the fifth 

 correction line, is a tract of about 43 townships in which the rock is mostly greenstone 

 and hornblende slates! This part of the surveyed district is less broken than that 

 above described, and a large proportion of it may be denominated rolling lands. 

 There are, however, many ridges and conical hills of various heights upon this part of 

 the survey, and also deep valleys of streams, many of which have ledges upon their 

 sides. These general characteristics are often changed for cedar, spruce, or tamarack 

 swamps, which are most numerous in townships 46, 47, and 48 IST. [This includes the 

 part of the district supposed to be the continuation of the northern Wisconsin 

 peneplain (p. 31).] 



