AMERICAN GEOLOGY— DECADE OF 1850-1859. 473 



even going - so far as to refuse to refund to Hall the money actually 

 expended by him for the purpose of the survey or to pay for his own 

 services. Under HalFs brief administration Whitney, who had served 

 in a like capacity in Iowa, was employed to complete the work on the 

 lead region and Charles Whittlesey to study the regions lying on 

 the west side of the Menomonee River and the iron region of Lake 

 Superior. 



A single royal octavo volume of 455 pages and 9 plates, a colored 

 geological map of the lead region, and a diagram showing the position 

 of the ore crevices, appeared in 1862 as a result of this organization. 



In this Hall repeated his attempts at correlation of the western with 

 the eastern formations. In addition he called attention to the driftless 

 area of the State, and to the fact that, over the whole area south of the 

 Wisconsin River, the Galena limestone and a portion of the underlying 

 Blue limestone had been removed by decomposition and solution to a 

 depth of some 350 to 400 vertical feet. 



Whitney, in his report on the lead-bearing region showed, as in his 

 previous work (p. 46S), that the lead-bearing fissures of the Northwest 

 were limited to one set of strata, and that there are but rarely any 

 evidences of dislocation of the strata or faults. Hence, he was forced 

 to the conclusion that the ore-bearing crevices originated through the 

 action of some local cause or forces which were limited in their field 

 of action to a comparatively narrow vertical range. In short, he con- 

 ceived the lead-bearing fissures to have been originally closely allied 

 to wdiat are called joints. How far shrinkage and crystalline action 

 may have been concerned in the production of these joints, he was 

 unable to say, but "It will be sufiicient at this time to recognize the 

 fact that either or both these causes united would have produced a 

 tension in the mass of rock which would lead to the production of fis- 

 sures in two different directions.'' He felt, further, that the direction 

 of the fissures might have been influenced, if not absolutely deter- 

 mined, by an elevatory movement of the region in which they are 

 developed. 



He looked upon these veins as having been filled from above, the 

 various metals having been in solution as sulphates in oceanic water 

 at the time of the deposition of the lead-bearing strata, the precipita- 

 tion as sulphides being brought about through the agency of sulphu- 

 reted-hydrogen gas, which was liberated by the decomposing organic 

 matter. This is substantially the view held by most authorities to-day. 

 He thought, further, to recognize a general law connecting the lack of 

 mineral deposits in the nonfossiliferous strata with their abundance in 

 those containing organic remains. As in his previous work (Metallic 

 Wealth of United States, p. 438), he differed with both Daniels and 

 Owen as to the metalliferous character of the lower magnesian rocks, 



