32 EXPLORING EXPEDITION FROM SANTA FE 



the Tertiary tufa; but, over large areas, it is itself the surface rock. At Whetstone 

 Creek this group is exposed iu the hanks of the stream, and shows a great number of 

 alternations of very fine-grained, laminated sandstone, with more argillaceous hands. 

 These strata contain fossil plants in large numbers, which would undoubtedly well 

 reward collectors who could have more time to devote to the locality than was at my 

 command. Several of the species noticed there are apparently different from those 

 obtained from outcrops of this formation from other localities, but a narrow leaf, per- 

 haps a Salix, seems to be identical with one obtained at Smoky Hill, Pawnee Fork, ivc. 

 A remarkable fissure has been opened by volcanic force in the rocks containing 

 these plants. It is aboiit four and a half feet wide following the main jointings of the 

 sandstones, which here run nearly east and west, No trap fills the fissure, but it is 

 evident that it was once a kind of flue through which a vast amount of heat escaped 

 from below. Its sides are blackened, glazed, and blistered, and the sandstone which 

 forms its immediate walls is considerably metamorphosed; to the depth of an inch it is 

 vitrified; back of this it is converted into a hard, blue, sonorous rock, resembling a 

 compact basalt, The effect of heat is noticeable in the changed condition of the sand- 

 stone several feet from the sides of the fissure, but at a distance of twenty feet the rock 

 again exhibits its normal appearance. 



VALLEY OF THE CANADIAN. 

 MIDDLE CRETACEOUS STRATA. 



The valley of the Red Fork of the Canadian is a broad eroded trough, excavated 

 almost entirely irt the great group of limestones and calcareous shales which rest upon 

 the sandstone group I have so frequently referred to as the Lower Cretaceous sand- 

 stones. The overlying calcareous mass, which contains immense numbers of Cre- 

 taceous fossils, is apparently the equivalent of Nos. 2, 3, and 4 of Meek and Hayden's 

 Nebraska section. 



In my former notes on the geology of this region, I designated this series as I 'pper 

 Cretaceous, to distinguish it from the Lower Cretaceous sandstone group. At that time 

 I had seen no evidence of the existence in New Mexico of higher members of the 

 Cretaceous formation. In our recent explorations of the San Juan countrv, where 

 this series is very largely developed, I- found the equivalents of the strata under con- 

 sideration covered by soft sandstones and marls, which I regarded as also members ol 

 the great Cretaceous formation. This latter group is, therefore, more properly I'pper 

 Cretaceous, and the calcareous strata of the Canadian and their equivalents will be 

 designated in the subsequent portions of this report as Middle Cretaceous. 



In describing the Cretaceous strata of the country bordering the San Juan, I shall 

 have occasion to return to the subject of the classification of the rocks belonging to 

 this series, as developed in New Mexico, and, as far as practicable, establish a. paral- 

 lelism between them and those of the Upper Missouri, as described in the Nebraska 

 section of Messrs. Meek and Ilayden. I may here say, however, that the division of 

 the ( 'retaceous rocks of New Mexico into three great groups Upper, Middle, and 

 Lower will be found to be the most convenient, if not the only one practicable 



