Stevenson] 4 ^ 1j [June 18, 



Thirdly, That the conditions observed in the Great Lignitic Group, are 

 but a repetition or continuation of those commonly observed in the Lower 

 Cretaceous and less frequently in the Middle Cretaceous. The sandstones 

 of the Lower Cretaceous, when unaltered, can hardly be distinguished 

 from those of the Lignitic series ; coal beds occur at both horizons ; while 

 on the Pacific Coast coal beds frequently occur in the Middle Cretaceous. 



Fourthly, That the fauna consists for the most pai't of marine or 

 brackish-water species. At the base of the series, in the great sandstone 

 (including No. 5), the species are all marine ; among the coal beds they are 

 usually brackish-water, while at the highest horizon found in Colorado 

 and New Mexico, they are marine. Here and there the fauna is a mixed 

 one, and at times, over no inconsiderable area, it consists solely of fresh- 

 water forms. There would be room for surprise were it otherwise. A 

 shore deposit, such as this must have been, would be exposed to the influ- 

 ence of salt and brackish water alternately. The slow subsidence might 

 be interrupted so as to permit the silting up of portions of the area, 

 where fresh-water ponds of considerable extent might be formed. 

 Such evidently was the case during the formation of the Coal Measures. 

 Dr. Dawson has found a mixed fauna in the South Joggins Coal Field, and 

 Mr. Meek obtained shells, closely allied to Piqya, from the upper coals 

 near Wheeling, W. Va. Unfortunately our knowledge respecting the 

 distribution of land and fresh-water forms during geological time is so 

 limited that we cannot trace out the history of genera with any degree of 

 satisfaction. No positive argument, bearing upon age, can be based 

 upon their presence in any group of rocks. 



FiftJily, That the fauna, wherever found, is Cretaceous, or of such a 

 character, as to render it neutral testimony, affecting the issue neither 

 in one direction nor the other. Throughout a large portion of the area 

 the fauna is lacking. That barren zones occur in the Upper Creta- 

 ceous was observed years ago, by Dr. Hayden, in the Upper Missouri 

 Region. The same is true of it throughout the whole Rocky Mountain 

 Region, north from New Mexico. But we must determine fauna by what 

 we have, not by what we have not. This we do in the Coal Measures, where 

 the barren zones are quite as remarkable as those of the Upper Cretaceous 

 in the Rocky Mountain Region, In the Anthracite area, animal remains 

 are rare ; in West Virginia, south from the Baltimore and Ohio Railroad, 

 where the Coal Measures are exposed to a thickness of not far from two 

 thousand feet, there is not a single stratum which is fossiliferous ; and in 

 the northern portion of the Great Bituminous Group, where the Coal 

 Measures are nearly three thousand feet thick, there are but two strata, 

 which jjersistently contain the fauna. Yet west from the Cincinnati axis, 

 over a vast area, animal remains occur profusely at numerous horizons 

 in the series. 



A similar condition seems to have existed during the formation of the 

 Lignitic Group. Near the old shore line, animal remains are rare, but as 

 we pass from that line, they become more numerous. It should be re- 



