M. R. Thorpe— The Abajo Mountains, Utah. 381 



the axis of which runs east and west, joins Shay mountain 

 and Mt. Linnaeus. The pitch of the axis is toward the 

 west and does not exceed 2° or 3°. The Dakota sand- 

 stone forms a dip slope on the south side of Shay Moun- 

 tain and the same on the north slope of Mt. Linnaeus. 



2. Mt. Linnceus (fig. 3) is a partially uncovered lacco- 

 lith. The Dakota sandstone overlaps the northeastern 

 section, but no lower formation is exposed, whereas on the 

 other sides of the mountain from 200 to 250 feet of upper 

 McElmo are upturned beneath the Dakota sandstone, 

 hence the horizon of intrusion is most probably middle 

 McElmo, except on the northeastern side. If the lower 

 Cretaceous and Upper Jurassic strata were projected 



Fig. 2. 



LEGEND 



m 



Sedimentary R o c .'< s 



Scale of Mile 



Hornblende -latite Porphyry 



over the mountain in accordance with the dips now found 

 they would form the cover of the laccolith with no difficul- 

 ties. Patches of the roof rock are present in several 

 places at all elevations on the mountains. 



3. The Southern Area. — The Dakota and Upper 

 McElmo formations flank the mountain sides to varying 

 heights so that these peaks are by no means well exposed 

 except near their summits. On the south and east sides 

 the Dakota slopes up with a gentle but constantly increas- 

 ing dip away from the mountains until it reaches well 

 up their flanks. Here the Dakota and Upper McElmo 

 formations unquestionably formed the cover at the time 

 of intrusion. On the eastern side several prominent 

 spurs extend outward and the dip of the strata flanking 

 them is as high as 45° east, although dips ranging from 

 35° E. to 41° E. are common. 



4. The Northern Area. — The horizon of intrusion in 

 the case of North and Twin Peaks as well as the western 

 part of Horsehead Peak was at or near the base of the 



