SUEVEY OF COLOEADO AND NEW MEXICO. 85 



The sectiou in desceuding order is as follows: 



1. Tertiary strata forming tlie greater part of the hill known as Mount 

 Bross. 



2. Gray laminated sandstones passing down into arenaceous clays 

 with BacuUtes ovatus, &c. 



3. Black clays of E"o. 4. These are of great thickness and every variety 

 of texture. As shown in a cut bank of the river it is yellow arena- 

 ceous clay with layers of sandstone, in which the impressions of deciduous 

 leaves were observed. These layers project up, a distance along the 

 bank, of seventy paces. 



4. Dark plastic clay with cone in cone, seams of impure clay, iron ore. 

 Then comes an interval in -which no layers could be seen, sufficient to 

 include Ko. 3 — two hundred and fifty paces. 



5. Dark steel-black laminated slate, with numerous fish scales; dip, 

 twenty-seven degrees. This slate passes down into alternate layers of 

 rusty sandstone and shaly clay'. 



In the upper bed of sandstone and shaly clay are obscure vegetable 

 impressions, leaves, stems, nuts, &c., evidently deciduous. In the upper 

 bed of sandstones are two or three thin seams of carbonaceous shale, and 

 the intervening layers of sandstone are almost made up of bits of vegetable 

 matter. Toward the lower, it becomes a hard mud rock i^assing down 

 into rusty yellow sandstone with all sorts of mud markings. Then comes 

 a bed of bluish plastic clay with sulphur and oxide of iron ; dip, thirty- 

 three degrees. Then rusty fine-grained gray sandstone passing down 

 into a very close massive pudcling-stone, composed of very smooth 

 nicely-rounded pebbles, cemented with silica. This stone would be 

 most excellent for building material and is susceptible of a very fine 

 polish. A fracture passes directly through the pebbles, the paste being 

 harder, if anything, than the inclosed pebbles; dip, thirty-one degrees. 

 This is a very thick bed and is a portion of Xo. 1, cretaceous, or a sort of 

 transition bed between the cretaceous and the Jurassic. 



The red and variegated beds lie fairly upon the gneissic granites, and 

 although they are shown very obscurely here, yet I think they must 

 exist, inasmuch as they are so well revealed not more than fifteen miles 

 east of this point, so that I have no doubt they are lost beneath the mass 

 of superincumbent material. I think the light-colored clays lying under- 

 neath the bed of chalky clay, are Jurassic. There is a bed of fine 

 gritty clay underneath the pudding-stone which would make excellent 

 hones. 



In the intercalated sandstones above the pudding-stones are plants 

 just like those observed in ISTo. 1 at Sioux City, on the Missouri Eiver, 

 and the composition of the strata is the same ; there is a Salix, a con- 

 iferous plant, the cones of a pine, &c. 



I have given this detailed description of the cretaceous rocks to show 

 the exceeding variableness of their texture, and also to call the atten- 

 tion of scientific men, who may hereafter visit this interesting locality, 

 which will soon become celebrated, to a section of the rock through 

 which the waters of the spring must pass in reaching the surface. ISTow 

 in whatever rocks these springs may originate, the water must pass a 

 long distance through the almost vertical strata of the cretaceous period, 

 in the sediments of which are found in other localities nearly all and 

 perhaps all the mineral constituents found in these springs. The deposits 

 around these springs are very extensive. IS'o analysis has as yet been 

 made, but large masses of gypsum and native sulphur can be taken out 

 at any time from the sides of the large basin-like depression into which 



