TRILOBITE POINT. 11 



the rock into hexagonal columns, which are well denned near the outside 

 of the dike, but disappear toward the center. The rock is dark colored 

 and dense near the contact walls, becoming lighter colored and less dense 

 toward the center, and containing irregular vesicular cavities, flattened 

 parallel to the walls of the dike. 



Direct connection between the -formations of this ridge and those of 

 the mountains north is obscured by the rhyolite lava which extends up 

 Winter Creek and across the saddle of the divide to Maple Creek. A close 

 correspondence, however, between the sections of limestones and the intru- 

 sive sheets is observed on both sides of Christmas Tree Park, and when the 

 dip of the strata in each case and the altitudes at which similar horizons are 

 exposed are taken into account, it appears that the rocks on both sides of 

 the valley were continuous, with low southerly dip, before the valley was 

 eroded and filled with rhyolite, or that a very slight fault has dropped the 

 strata of the ridge just described a few hundred feet. In the diagram of 

 cross sections, PI. Ill, fig. 1, the strata are drawn as though not faulted. 



TRILOBITE POINT. 



At the south and east base of the group of peaks directly connected 

 with Mount Holmes, including Trilobite Point and The Dome, crystalline 

 schists are exposed at altitudes of from 8,000 to 8,500 feet, and in isolated 

 localities at 8,700 feet. These outcrops form a low, rounded bench at the 

 base of the mountains, the upper limit of the gneiss being highest at the 

 south, and lowest in elevation north, in the bottom of Indian Creek. The 

 isolated exposures near the head of Winter Creek are close to the margin of 

 the great intrusive mass of Mount Holmes, and, though at about the same 

 altitude as the other outcrops, show by the dip of the neighboring stratified 

 rocks that their position has been disturbed by the intrusion of this igneous 

 mass. The limestones dip steeply in various directions, and the beds are 

 largely concealed by drift, the outcrops being small and disconnected, so 

 that the precise stratigraphic structure was not apparent at this locality. 

 The map represents the beds as continuous with those to be described in 

 Trilobite Point, though they are in fact locally disturbed by the intru- 

 sion of the Holmes mass. 



The character of the crystalline schists is like that of the area about 

 The Crags — coarse-grained gneisses, mostly micaceous, with subordinate 



