GEOLOGICAL SUKVEY OF THE TEREITORIES. 153 



feet high, the rocks being of a dark steel-gray color. There is no evi- 

 dence that the underlying strata have been disturbed by this butte. 



The evidences of igneous protrusions are everywhere abundant, south 

 of this point, for two hundred miles. The Spanish Peaks I regard as a 

 gigantic dike, with the strike about northeast and southwest. The entire 

 surface of the country, from the Spanish Peaks to the Eaton Mountains^ 

 is penetrated with dikes, which often reach far across the country with 

 a trend about northeast and southwest. The cretaceous rocks are in 

 many places much changed by contact with the fluid mass, and in some 

 cases the strata are somewhat disturbed. The clays are turned into 

 slates and the sandstones into dark steel-colored rocks, much like the 

 basalt itself. In No. 2 1 found a species of Inoceramus, very distinct, and 

 a Modiola. 



About ten miles before reaching the Apishpa Creek the tertiary sand- 

 stones begin to show their abrupt blufts on our right. 1 am convinced 

 that beds of this age entirely surround the Spanish Peaks and the 

 mountains in the vicinity. This abrupt front continues north of the 

 Eaton Mountains until we come to Trinidad, and presents a singular feature 

 in the scenery. It would seem to form a sort of a shore line of a won- 

 derful basin, as if a body of water had swept along and washed against 

 these high bluffs, as along some large river. That these beds once ex- 

 tended far out into the plains eastward, seems clear, and the evidences 

 of erosive action are enormous. Here, abrupt bluffs which form these 

 different shore lines are four hundred to sis hundred feet high above the 

 creeks, and the dip of the strata is about five degrees west or southwest. 

 In the plains to the eastward are isolated mesas, which are left as monu- 

 ments to show that these beds, with the igneous outpourings, once extended 

 over a large part or all of the space to the eastward, which now looks so 

 finely leveled oft' like a meadow. This wall-like front extends sixty or 

 eighty miles in a nearly direct line southward, capped with a thick bed 

 of basalt, for the most part. 



Just east of the Spanish Peaks a distinct synclinal can be seen in the 

 tertiary beds. They dip slightly froiii the peaks, and from the bluffs 

 they dip gently toward the peaks, enough to produce a distinct depres- 

 sion of considerable length. I do not know why the tertiary strata 

 incline toward the mountains, unless they have been partially elevated 

 by the dikes. 



As far to the southward as the eye can reach, the country looks rugged 

 and mountainous, with some curious mesa-like summits covered thickly 

 with the piilon. These tertiary beds are composed as usual of alternate 

 beds of rather yielding sandstones of all textures and composition, with 

 clays, some of which are carbonaceous. The harder beds project out 

 from the sides of the hills, while the softer beds are smoothed off and 

 covered with grass or other vegetation. 



Near a stage station, about ten miles south of Apishpa Creek, the creta- 

 ceous clays, No. 2, are cut through by a small creek, so as to reveal three 

 dikes within the space of thirty feet. The first is Avell defined ; four inches 

 wide, vertical, looking like a stratum of dark brown sandstone standing 

 perpendicular; strike twenty degrees north of east. Second dike, strike 

 northeast and southwest; four feet wide. Third dike, northeast and 

 southwest, from twelve to eighteen inches wide. The clays are not dis- 

 turbed, and are perfectly horizontal, but so changed on each side of the 

 ilike that the cleavage has the appearance of stratification. I am con- 

 vinced that in the case of these small dikes the melted material has been 

 thrust up through the cleavage openings. There are very many dikes 

 in this region, all of which have a similar direction. I suspect that in 



