532 REPORT OF NATIONAL MUSEUM, L904. 



Le Conte's views, as shown in this report, concerning the general 

 development of the western portion of the continent, indicated an 

 ability to deal with the larger problems of geology in a philosophical 

 and highly satisfactory manner, and it is perhaps to be regretted that 

 he should have allowed himself to be drawn oft' into other pursuits. 

 As noted, this paper was the most important of his geological writings, 

 as it was also the last. 



The second geological survey of Iowa was inaugurated in April, 



lSOti, with Dr. Charles A. White as director, and Orestes St. John, 



principal geological assistant. The survey continued to the end of 



1869, results being published in the form of two royal 



iowa te 1866^1*869? octavo volumes, comprising all told some 443 pages, 



with a colored geological map of the entire State. 



As Hall and Whitney had devoted a large portion of their attention 

 during the previous survey to the eastern part of the State, so White 

 devoted himself mainly to an investigation of the phenomena of the 

 western part. He found reason, as noted in his introductory letter to 

 the governor, to discourage all explorations for mineral oils or precious 

 metals in the State, and also pointed out the hazard of exploring for 

 coal beyond the northern and eastern boundaries of the coal held as 

 designated in his geological map. He also showed that, though iron 

 ore of a good quality had frequently been found in the State, the 

 deposits were always limited. In all of these points he was correct. 



Considerable attention was given to the peat deposits and an esti- 

 mate made of the amount of material within the State limits which 

 could be utilized for fuel purposes should occasion demand. 



Among the phenomena of lesser importance he called attention to 

 the moving of the bowlders on the shores of lakes and piling them 

 into wall-like masses through the expansive action of the freezing- 

 water. The so-called Bin ft' deposit he considered to be of more recent 

 origin than the drift, and referred it to the earliest part of the so-called 

 Terrace epoch, the material composing it having originated by fliuvia- 

 • tile erosion immediately upon the close of the Glacial epoch, being 

 afterwards deposited as a lacustral sediment in the broad depression in 

 the surface of the drift left by the retreating glaciers. He differed 

 entirely with Whitney as to the cause of the absence of trees in the 

 prairie region, and felt no hesitation in declaring that the real cause 

 of the existence of the prairies in Iowa was the recurrence of the 

 annual tires. 



He divided the formations of the State into Azoic, Lower Silurian, 

 Upper Silurian and Devonian, Carboniferous, and Cretaceous systems, 

 and regarded the Sioux Falls quartzite, with its associated pipestone, 

 as belonging to the Azoic. The Potsdam sandstone, which he found 

 reaching a thickness in the State of about 300 feet, he thought to be 

 probably overlying this Sioux quartzite. This view is generally held 

 to-day. 



