538 report of national museum, 1904. 



or, at best, the very poor ones furnished by the Land Office, no rail- 

 roads, and transportation was limited to canoes and pack animals. 

 There were few prospect holes and fewer developed mines. To these 

 difficulties were added the complications due to repeated folding- and 

 squeezing which the beds had undergone. Yet Brooks, by his per- 

 sistency and originality in methods, succeeded in producing a work 

 of value as a scientific production as well as of the greatest use to the 

 prospector — a rare combination, indeed — and a work which has been 

 superseded only by one that it took twenty years of study by an able 

 corps of geologists and a hundredfold better facilities to produce. 



Brooks devised the dial compass and adapted the dip needle to the 

 purposes of the prospector. Persistent and determined to succeed in 

 spite of the poverty of appropriations, he expended over $2,000 of his 

 own means and, worst of all, sapped his own vitality in the work to the 

 extent that he became a confirmed invalid before reaching middle age. 



As already intimated, his health gave out in 1873 and he sought 

 relief abroad, residing in London and Dresden, where his reports were 

 completed. After his return to this country in 1876, he resided at 

 Monroe and Newburgh, New York, and after 1883, during the winters, 

 at Bainbridge, Georgia, living the life of a country gentleman and 

 farmer. 



Pumpelly's work in the copper district is of interest on account of 

 „ , „, „ his theories regarding the origin of the copper and the 



Pumpelly's Work . . 



'" ^"ch'gan, a g e anc l lithological nature of the copper-bearing rocks. 



The conclusions at which he arrived were as follows: 



First, the cupriferous series was formed before the tilting of the Huronian beds 

 upon which it rests conformably, and consequently before the elevation of the great 

 Azc lie area, whose existence during the Potsdam period predetermined the Silurian 

 basins of Michigan and Lake Superior. Second, after the elevation of these rocks 

 and after they had assumed their essential lithological characteristics, came the depo- 

 sition of the sandstone and its accompanying shales, as products of the erosion of 

 these older rocks, and containing fossils which show them to belong to the Lower 

 Silurian, though it is still uncertain whether they should be referred to the Potsdam, 

 Calciferous, or Chazy. 



A chapter was given on the paragenesis of copper and its associates. 

 With reference to these subjects he wrote: 



It is still an open question whether the trap which formed the parent rock of the 

 melaphyr was an eruptive or a purely metamorphic rock. If it was eruptive, it was 

 spread over the bottom of the sea in beds of great regularity and with intervals which 

 were occupied by the deposition of the beds of conglomerate and sandstones. It 

 should seem probable that the copper in the melaphyrs was derived by concentra- 

 tion from the whole thickness of the sedimentary members of the group, including 

 the thousands of feet of sandstones, conglomerates, and shales which overlie the 

 melaphyrs, and including melaphyrs also. 



The translocation he regarded as having been initiated by the sul- 

 phate of copper resulting from the oxidation of the sulphide, but as 



