SURVEY OF COLORADO AND NEW MEXICO. 1& 



The opening in tlie foot-hills of the nionntains through which Box 

 Elder Creek flows exhibits the red beds and Jurassic in full development. 

 The whitish-gray sandstones, which lie between the red beds and the. 

 well-marked cretaceous strata, contribute much toward giving sharp- 

 ness of outline to the hills, and the broken masses of rock from this bed 

 are scattered over their sides. 



The valley of the Box Elder is very beautiful, and, like the valleys of 

 most of the little streams here, makes its way through the ridges and 

 flanks of the mountains, nearly at right angles to the trend of the strata. 



All these ridges, or "hog-backs," as they are called by the settlers of 

 the country, vary much in the angle of dip. It not uufrequently occurs 

 that the outer and more recent ridges incline at a very high angle, or 

 stand nearly vertical ; and there are many examples where they have 

 been tipped several degrees past verticality ; while the inner sandstone 

 ridges, lying almost against the metamorphic rocks, incline at a small 

 angle or are nearly horizontal ; and again this may be reversed. These 

 mountain valleys are not only beautiful, but they are covered with ex- 

 cellent grass, making the finest pasture grounds for stock in the world. 

 The animals are so sheltered by the lofty rock- walls on each side that 

 they remain all winter in good condition without any further provision 

 for them. 



The Box Elder separates into two brauches in the foot-hills, and be- 

 tween the forks there is a large circular cone with nearly horizontal 

 strata of the red beds. A section, ascending, would be as follows: 



1. Brick-red sandstone with irregular lamiiise and all the usual signs 

 of currents or shallow water. Some of the layers are more loosely lami- 

 nated than others, thus causing projecting portions — 300 to 400 feet. 



2. The red sandstone passes up into a yellow or reddish-yellow sand- 

 stone, massive — GO feet. 



3. Passing up into a bed of grayish yellow rather massive sandstone — 

 50 feet. 



4. Ashen-brown nodular or indurated clay, with deep, dull jjnrple 

 bands ; with some lasers of brown and yellow fine-grained sandstone, 

 undoubtedly the usual Jurassic beds with all the lithological characters 

 as seen near Lake Oomo, on the Union Pacific railroad — 150 to 200 feet. 



IsTear the base of these beds are thin layers of a fine grained grayish 

 calcareous sandstone, with a species of Ostrea and fragments of Penta- 

 crinus asteriscus. Scattered through this bed are layers or nodules of 

 impure limestone. 



5. Above this marly clay there is at least two hundred feet of sand- 

 stone and laminated arenaceous material, varying in color from a dirty 

 brown to grayish white, with layers of fine grayish-white staudstone. 



I do not hesitate to regard the beds described as 4 and 5 as of Jurassic 

 age, and they are better shown here than at any other point between 

 Fort Laramie and the south line of Colorado on the eastern slope of the 

 Eocky Mountains. Usually the most abundant and most characteristic 

 fossil in the Jurassic beds, when exposed, is Belemnites densus, but that 

 has not been observed south of Lake Como, w^est of the Laramie range. 

 As w'e proceed southward these Jurassic beds become thinner and more 

 obscure, so that it often becomes a matter of doubt whether they exist 

 at all. 



We have, also, in this vicinity an illustration of the difference of in- 

 clination in the same series of upheaved ridges. In the plains some of 

 the low^er lignite tertiary beds and cretaceous 1:^0. 5 stand nearly ver- 

 tical, or 85° east. No. 4 fills the intervening valley with its dark shale, 

 and the next ridge west — cretaceous No. 3 — inclines 30°. Then come 



