case: a geological reconnoissance. 145 



river. The beds are cross-lined in every direction by thin layers 

 of impure gypsum, with occasionally one eight or ten feet in thick- 

 ness, occurring as low down as the middle af the formation. The 

 upper layers in these beds have in some cases been hardened by 

 infiltration of silica from the Tertiary, and stand out in overhanging 

 shelves from the softer limestone below, very much as described and 

 figured by Hay in his article on this formation further east. 



In one place, about half way between Beaver City and Alpine, 

 there is a bluff, some twelve feet high, composed of coarse conglom- 

 erate, the layers of which show the irregular stratification of beach 

 formations. Other less well marked instances of this beach stratifica- 

 tion are not infrequently met with. 



The extreme irregularity of the strata renders any very accurate 

 account of the successive layers a matter of difficulty, but, in general, 

 there is first the Tertiary grit, below, a layer of laminated flint over- 

 lying a thick bed of impure limestone five or six feet thick, and filled 

 with shells of Planorbis. Under this, more flint, containing shells 

 and impressions of reed-like leaves. Lowermost of all, is the chalk 

 having the leaf impressions. There are, besides, several layers of 

 sandstone, all so thin and irregular in their outcroppings as to make 

 their true relations doubtful. The Trias has first the thick red sand- 

 stone interlined with gypsum in its upper portions; then several layers 

 of sandy shale, alternating with sands of a yellow or black color 

 and friable red sandstone. These black sand-beds have been the 

 subject of some little local excitement, as possibly gold-bearing. 



The chalk appears in limited outcrops for about thirty miles along 

 both sides of the Beaver, at a distance of three or four miles from the 

 immediate river valley. The chalk is fairly homogeneous in compo- 

 sition, some portions being a little more coarse than others, probably 

 due to a variable percentage of silica. Some of the upper layers 

 have a conchoidal fracture. All the outcrops are capped with flint 

 in layers and nodules, the nodules are also interspersed throughout 

 the chalk. The flint frequently contains impressions of leaves, but, 

 owing to its peculiar fracture, it is difficult to obtain good specimens 

 from it. The largest bed of chalk though not the richest in speci- 

 mens, is that on the south bank of the Beaver, about four miles up a 

 small tributary, called "Gypsum Creek." It dips abruptly to the 

 west and north, and is thickly covered with flint and Tertiary debris. 

 Near the upper surface of the chalk are two seams, each about six 

 inches thick, filled with shells and impressions of reed-like leaves, 

 evidently aquatic. The matrix is a sandy, carbonaceous material, 

 mixed with flint nodules. Cragin found in these layers a tarsal bone, 

 which he referred to the Cavielidce. The remainder of the chalk is 



