AMERICAN GEOLOGY DECADE OF 1800-1869. 588 



White regarded it as evident that there was no hope of profitable 

 lead mining within the limits of the State in the Lower Magnesian 

 limestone, in this agreeing with Whitney (p. 408). For the so-called 

 Hudson River shales of Hall he substituted the name of Maqnoketa 

 shales. All the Devonian rocks of the State he referred to the Ham- 

 ilton period. 



He found a strict conformability in all the rocks from the Potsdam 

 sandstones to the Keokuk limestone, inclusive, but between this last 

 and the rocks of the Coal Measures an unconformability and also one 

 between the St. Louis limestone and the older formations of the sub- 

 Cretaceons group. Instead of there being only one formation of Car- 

 boniferous limestone, as had been generally supposed, White claimed 

 to have found two, each possessing similar lithological but different 

 paleontological characteristics, the one overlying and the other under- 

 lying the coal-producing strata. 



The various folds found in the strata of the Iowa rocks he regarded 

 as all having taken place subsequent to the deposition of the latest 

 strata of Carboniferous age and before any of those of Cretaceous age 

 were deposited. 



The gypsum deposits were thought to be presumably of Mesozoic 

 age and as having originated through chemical precipitation in com- 

 paratively still waters which were saturated with sulphate of lime and 

 destitute of life. The fact that these deposits contained no fossils 

 rendered the exact determination of their geological age a matter of 

 some difficulty. It is therefore well to note that Kcyes in his report 

 in 1895 refers them to the upper part of the Mesozoic — the Cretaceous.' 



White, it should be noted, had in I860 6 described in considerable 

 detail the rocks and their included fossils in the vicinity of Burling- 

 ton, Iowa. He identified here eight beds, the lower six of which he 

 regarded as the equivalent of, though not necessarily contempora- 

 neous with, the Chemung of New York. The two upper beds, which 

 were of limestone, he regarded as Carboniferous, though he remarked 

 that the line drawn between the two formations was largely imagi- 

 nary, indicating merely the limit where the Devonian species ceased to 

 predominate and upward from which the Carboniferous species 

 flourished in full force. 



It was suggested that the Devonian species might have originated 

 at the east and migrated westward during the time that the bottom of 

 the Chemung sea was gradually sinking and receiving the deposits 

 forming the Old Red sandstone, thus making the Devonian rocks 

 equivalent to the New York Chemung and contemporaneous, in part 

 at least, with the Old Red Sandstone of the Catskill Mountains.** 



"Report of the State Geological Survey of Iowa, VII, 1895. 

 ''Boston Journal of Natural History, VIII, 1859-1863, pp. 205-235. 

 c All of the six beds then supposed to bs Devonian are now commonly regarded as 

 belonging to the basal Carboniferous ( Kinderhook). 



