336 



G. K. GILBERT AND F. P. GULLIVER — TEPEE BUTTES. 



exposures measure 12, 13 and 18 feet respectively. The more or less 

 plausible assumption that all members of a certain group have their 



bases at the same horizon leads 

 to the inference that one of them 

 was originally more than 30 feet 

 high. The observed facts would 

 consist with a general height of 

 25 feet, and perhaps equally well 

 with a general height of 100 or 

 200 feet. 



In horizontal cross-section 

 they are rudely circular or ellip- 

 tical, the ratio of the axes being 

 seldom greater than 4 to 3. The 

 smallest observed core measures 

 2 feet across ; the largest, 24 by 

 21 feet. The ordinary diameter 

 is 10 or 15 feet. 



While the general form is prop- 

 erly defined as cylindrical, it is 

 far from regular. Wherever part 

 of a side was seen it was found 

 to exhibit shoulders, shelves and overhangs, besides being rugose in 

 detail. 



The passage from limestone to shale is abrupt, in the sense that there 

 is no intermediate material sharing the characters of both ; but there is a 

 certain amount of interpenetration. Processes of the limestone embrace 

 portions of shale, and the contiguous shale contains outlying lumps of 

 the limestone. The limestone is divided into beds, either completely or 

 approximately, b}^ horizontal partings of shale, so that the best exposed 

 cores have a stratified appearance. The general thickness of these beds 

 is from 1 to 3 feet (see figure 3 and plate 17). 



In the shale close to the core are also concretions of a special type, quite 

 different from the ordinary concretions of the Pierre shale. They are but 

 a few inches in diameter, are usually devoid of fossils, and are character- 

 ized by smooth processes after the manner of the loss-manchen. 



THE TEPEE ROCK. 



The tepee rock is essentially a calcium carbonate, the ratio of calcium 

 carbonate to magnesium carbonate being 18 to 1 in the single sample 

 analyzed. That sample contained also 12 per cent of argillaceous ma- 

 terial. For comparative purposes analyses were also made of the inclos- 



FiGURE 3. — Ideal Section through Tepee Core. 

 •Showing relations to shale and concretions. 



