Stevensou] 4Uo [June 18, 



obscure fragment of a marine bivalve, like the clam, while in the mud- 

 beds and shales below, species of Inoceramus are common."* In the 

 Raton Pass, Dr. Leconte found a small Inoceramus, badly preserved, as 

 would naturally be expected by any one familiar with the rock. Major 

 Hawn, in his report to Lieiit. Ruffner, says that he obtained Cretaceous 

 fossils near Canon City at only a few feet below the coal. Above this 

 sandstone, in the shales among the coal-beds, there are several layers 

 crowded with an Ostrea of undetermined species. 



Along the South Platte, about forty miles north from Denver, there 

 occurs a great mass of sandstone which, in my report to Lieut. Wheeler, 

 I have regarded as the great fucoidal sandstone. Mr. Arnold Hague, who 

 explored this region with much care in connection with the Geological 

 Survey of the Fortieth Pai-allel, maintains that the sandstones belong 

 not at the base, but at the very top of the Lignitic Group. He is doubt- 

 less correct. The section, as I followed it, begins at the mouth of St. 

 Vrain's Creek and continues without a break to Evans and Greeley, a dis- 

 tance of about twenty miles. The dip in this direction is quite small, 

 as the road crosses the true dip. My examination here was a hasty one, 

 and I had no opportunity to follow up either St. Vrain's or Thompson's 

 Creek, so as to ascertain what underlies this rock. The whole mass cer- 

 tainly overlies the thin lignites of Platteville. The clays and sandstones 

 seen below the sandstones at the mouth of St. Vrain's bear much resem- 

 blance to those below the fucoidal sandstone at Canon City, and this in- 

 duced me to regard the section as the same. But a careful comparison 

 and summing up the sections, shows me that the total thickness, several 

 hundred feet, is far too great to permit us to suppose it the fucoidal sand- 

 stone, and we must therefore regard it as belonging much higher in the 

 series, f 



These sandstones are several hundred feet thick, light-bluish-gray to 

 reddish-brown and yellow, and rest on a mass of clays and shaly sand- 

 stones. They are all friable and yield readily to the weather, wearing 

 into immense cavities and breaking down into loose sand. In the red- 

 dish ferruginous sandstones, which form the top of this group, there are 

 many thin argillo-calcareous layers, which are prodigiously rich in fossils. 

 Some of these are simply masses of the fucoid, Halymenites major, Lesqx, 

 while 'others contain characteristic species of Cretaceous No. 5, such as 

 Ammonites lohatus, Gardmm speciosum, Nucula cancellata, Mactra alia, 

 Mactra Warrenana, Lunatia Moreauensis, and undetei'mined species of 

 AncTiura. The same species were obtained from this vicinity in 1874, by 

 a party under the direction of Dr. Hayden, to whom I had minutely des- 

 cribed the locality. 



From the interior of New Mexico we have but little information re- 

 specting this group. Much material has been gathered, but it is unpub- 



* Reprint of Reports, p. 154. 



1 1 understand that Dr. Newberry proposes to visit Colorado this year. He will ex- 

 amine this vicinity closely. 



