388 Mar cons Geological Map of the United States. 



similarity indicates a Carboniferous age rather than Triassic, 

 The limit of the formation above or below, although perhaps 

 well defined at one point, may not be at others, or may be very 

 different ; the red color of the strata — the only guide — being the 

 result of chemical changes and not of original deposition. The 

 lower limit is not clearly defined, and there are no outcrops 

 or uplifts of the strata sufficient to reveal the whole series. The 

 thickness, therefore, cannot be accurately stated. 



The entire absence of fossils from these strata, so far as known, 

 and our slight knowledge of the line of separation between 

 them and those of known age, and the impossibility of deter- 

 mining their thickness, render it premature, at least, to assign 

 them to the age of the Trias, and to partition them into groups 

 corresponding to those of the formation in Europe. We may 

 with equal reason call the strata Jurassic, Liassic, Triassic and 

 Permian, or either of them, as Triassic alone. It would be most 

 in accordance with the indications to refer them to the Cretace- 

 ous and Carboniferous, the two adjacent formations above and 

 below. 



But even if the gypseous strata along the Canadian were 

 proved to be of Triassic age, it does not follow that those along 

 the Upper Missouri, a thousand miles away, are of the same 

 period. According to published reports the strata along the 

 river are Cretaceous, and there is no evidence of the presence 

 of the Trias. Neither is there any evidence of the extension of 

 the Lake Superior sandstone across Wisconsin into Iowa and out 

 to the Missouri, as if the formation occupied an east and west 

 valley in the granite. Such a representation is at variance with 

 published records, and these surely should be regarded in the 

 absence of personal observation. It is hardly necessary to state 

 that the sandstone of Lake Superior has been examined by three 

 separate geological corps, — Messrs. Whitney and Foster with 

 the assistance of Prof. James Hall, by D. D. Owen, and by Sir 

 W. E. Logan of Canada — and after several years of exploration 

 in that region, all arrive at the conclusion that the sandstone is 

 not the New Eed, but is the equivalent of the Potsdam sand- 

 stone of New York. Prof. James Hall has announced the con- 

 clusion also in a notice of a former map by Mr. Marcou. 



There is here a disregard of published results and an auda- 

 cious attempt at generalization which has seldom been equalled. 

 The fact that Mr. Marcou's map is widely circulating in Europe 

 just such American Geology as this, has made it the duty of 

 the science of the country to protest against its being accepted 

 abroad, notwithstanding its publication under the sanction of the 

 Greological Society of France. 



