166 GEOLOGICAL SURVEY OF THE TERRITORIES. 



to Anthracite Creek. Its hardness has preserved it while the surround- 

 ing rocks have been removed. Its summit presents a ragged edge, spire- 

 like processes rising from it. The rock is very much like that of Mount 

 Marcellina, and that of areas described under A and A'. The dike g h 

 has a course almost at right angles to the one described. 1 was unable 

 to visit it, but am inclined to think it a continuation of the one marked 

 a 1). Other dikes in this region are shown, but were not visited. They 

 by no means represent all the dikes that are to be found, but merely the 

 principal ones. The mass of mountains north and east of station 32 

 contains many more that we were unable to define. 



C. — The center of this area is Mount Marcellina, a steep mountain, the 

 general shape of which is sugar loaf. It is shown at a in Plate XI. 

 This is probably the mountain to which Lieutenant Ruffner gave the 

 name of Mount Huxley,* as it answers the description. On the map 

 accompanying his report, however, Mount Huxley is marked as being on 

 the opposite side of the creek. It being, therefore, somewhat doubtful, 

 we have used the name Marcellina applied to it by prospectors that we 

 met in this region. The slopes are very steep, and the base surrounded 

 by a mass of debris. The sides are weathered into conical, spire-like 

 forms which stand out in bold relief, especially on the western and 

 southern sides. It is 11,324 feet above sea-level, and about 3,000 feet 

 above the top of the sandstones that form the surface between it and 

 the area marked D on the map. It is over 4,500 feet above the level of 

 Anthracite Creek, on the northwest side. The trachyte of Marcelliua is 

 very fine-grained, resembling closely the eruptive granites of the Elk 

 Mountains. On the northwest side of the mountain the Cretaceous 

 layers are tipped up, dipping to the northwest 15° to 20°. This is the 

 only point at which any disturbance of the strata around the mountain 

 could be seen. Here also they are penetrated by dikes of the same 

 material of which the main mass is composed. It was perhaps more 

 porphyritic. Plate XII represents three of these dikes on the south- 

 west side of the creek. On the opposite side there is a much larger 

 mass of this rock resting on the sandstones. I think it probable that 

 tne trachyte extends from Marcellina to the north side of Anthracite 

 Creek. Whether it extends to the westward connecting with C I am 

 not so certain. I have indicated the intermediate portion by dotted 

 lines. We did not have time to follow Anthracite Creek throughout 

 its entire length. 



U. — This area is the second in size, and comprehends 25 or 30 square 

 miles. It consists of a number of sharp peaks connected by sharp 

 ridges bounding amphitheaters in which rise streams tributary to Rock 

 Creek on the north and east, and on the south and west flowing to the 

 North Fork of the Gunnison. The western side of this mass is very 

 steep, the angle of the slope being about 50°. The summits are from 

 2,000 to 2,500 feet above the general level surrounding the mass. This 

 western side is not broken up by gullies. It preserves a uniform wall- 

 like surface for nearly three miles. The amphitheaters that we have 

 referred to are found on the southern and eastern sides, the majority of 

 the drainage being into Rock Creek. The eastern side is therefore most 

 irregular and shows most markedly the effects of erosion. Rock Creek, 

 opposite station 33, before it bends to the northward is 5,000 feet below 

 the summits of the peaks. The rock of station 33 is similar to that of 

 Marcelliua, the only difference being that the component parts in the 

 former are much coarser. . 



At I)' and D" there are two areas whose limits I am unable to define 



* Report of Reconnaissance in Ute Country, p. 41. 



