CENTURY OF IOWA GEOLOGY 417 



York rock-scheme and nomenclature to our state.". Hall was not 

 entirely unfamiliar with the western field. Some time previously he 

 had made an extensive geological trip through the upper Mississippi 

 valley with the special ohject in view of extending the New York 

 System. He had already the aid of Nicollet, Ow^en and others, 

 who had established a close parallelism between eastern and west- 

 ern sections. So, when he reached Iowa, as state geologist, matters 

 were already disposed very much to his liking. 



In introducing the New York classification into Iowa Hall appears 

 to have displayed the same intense prejudice against the new Eng- 

 lish scheme that he did a decade earlier in his eastern reports. There 

 is no mention of the English systems in his table of geological for- 

 mations. The noting of them on the accompanying map seems to 

 have been done by other hands. For many years the New York- 

 formational names given by Hall to western terranes were much in 

 evidence in the geological literature on the region. Gradually these 

 titles were displaced as unsuitable, until at the present time few of 

 them remain. 



But the English scheme proved fundamental and in its essentials 

 was adopted the world over. 



DETERMINATION OF THICKNESS OF IOWA ROCK FORMATIONS 



The conspicuous service which Dr. C. A. White rendered the 

 state was the determination of the thicknesses of the various geolog- 

 ical formations. In the main these figures were reasonably correct. 

 Without any deep-well records to serve as checks on the estimates 

 the results are often surprisingly close. The vertical extent of the 

 Cretacic rocks of the northwestern parts of the state and of the coal 

 measures of the southwestern portions are especially noteworthy.^^ 



The great economic value of White's estimates of rock thick- 

 nesses was, of course, the purposes which they served in furnishing 

 clues to local underground geology. They were especially helpful 

 in a region so deeply mantled with glacial drift as Iowa is. As 

 guides to boring deep wells for artesian waters, to prospecting for 

 coal and to search for other mineral wealth deeply hidden, their 

 wide serviceability was in after years recognized by the present 

 state survey and similar work was entered into exhaustively. White's 

 work served its purpose for a period of more than twenty-five years, 

 until newer figures could supplant the older ones. 



i^Geology of Iowa, 2 vols., Albany, 1858. 

 "Geology of Iowa, 2 Vols., Des Moines, 1870. 



