HISTORICAL SKETCH. 



specimens of large orthocera, fragments of which measure a foot long and more than four inches wide. 

 The faces of some of the rocks are covered with fuci, and in some producta form almost the body of the 

 rock. These fossil iferous beds are separated from the great sandstone beds of the country, which here go 

 far below the level of the river, by a thick stratum of eighteen feet of compact subcrystalline limestone 

 without fossils. Below this stratum nothing but sandstone appears." (Pp. 135-136.) He thus corrects 

 Keating's report (1S23), in which it is said that a limestone formation underlies the sandstone at Fort 

 Saelling. At St. Anthony falls "the immense slabs which have fallen from the limestone beds at the 

 top are covered with producta, mixed with spirifers and cardia. ***** To a geologist, however, 

 it is exceedingly interesting, finding here the uninterrupted continuation, for one thousand miles, of the 

 Carboniferous limestone, with its characteristic fossils." (Pp. 136-137.) 



David Dale Owen. 

 (Iowa, Wisconsin and Illinois.) 



1839. Report of a geological exploration of part of Iowa, Wisconsin and Illinois, made 

 under the direction of the Secretary of the Treasury of the United States, in the autumn of the year 

 183f>, by DAVID DALE OWEN, M. D., principal agent to explore the mineral lands of the 

 United States. 28th Congress, 1st Session, Senate document, 407, pp. 9-191, 1844. (Also 26th 

 Congress, 1st Session, House of Representatives, document 239, pp. 9-161, 1845. The 

 report was originally submitted for publication April 2nd, 1840, and was printed without 

 the accompanying maps, charts, sections and other illustrations, June 4th, 1840. The fore- 

 going editions were issued after the revision of the original, and the addition of some 

 statistics and of all the accompanying illustrations. ) 



This report is confined almost exclusively to the lead region. The lead-bearing rock 

 is embraced in the "Cliff limestone" which the author shows bears many points of similarity 

 to the Carboniferous lead-bearing limestone of England. Notwithstanding this outward 

 resemblance the organic remains require its assignment to a lower stratigraphic horizon. 

 In the "Cliff limestone" Owen here includes a thickness of 500 feet of strata, extending 

 from (and including) the Upper Silurian to the bottom of the Galena and Lower Silurian. 

 He shows that this great member passes below the Coal Measures, instead of above them as 

 thought by Keating, and is probably the equivalent of the Upper and perhaps of the Lower 

 Silurian of Murchison, and of the Corniferous, Onondaga and Niagara limestones of New 

 York, "and in part, perhaps, of the Champlain division." The fossils of the underlying 

 Blue limestone he considers closely like those of the Caradoc formation of England, and 

 of the Trenton limestone and shales of the New York system. This is the first suggestion 

 of the Trenton limestone in the valley of the upper Mississippi, but it should be datedfrom 

 the publication of his revised report, 1844. 



"The most characteristic fossils of the cliff limestone of Iowa and Wisconsin are: (p. 25.) 



"Casts (often siliceous) of several species of terebratulm. Some of them, probably, of new species. 

 These are chiefly confined to the upper beds. They are numerous and very perfect. 



"Several species of catenipora (chain coral) in greater abundance, and in more perfect preservation, than 

 I have ever seen them elsewhere; among them the catenipora escharoides of Lamarck; the catenipora laby- 

 rinthica of Goldfuss; and another species, not described by Goldfuss, nor elsewhere that I have seen prob- 

 ably new. I name it the catenipora verrucosa. * * * * These catenipora are very characteristic of the 

 upper beds of the cliff limestone. They do not occur in the rich lead-bearing strata. 



"A coscinopora (the sulcata? of Goldfuss), the only coralline discovered in the middle and lower 

 beds, and therefore characteristic of the true lead-bearing rocks. 



"Several species of calamopora, columnaria, tubipora, aulopora, sarcinula (costata?), aslrea, cyatho- 

 phylla, and caryophylla. These are found with the chain coral in the upper beds. 



