4()0 DESCRIPTIVE GEOLOGY. 



narrow ridge which forms the extreme point of the range is made up of 

 nearly horizontal beds of limestone, abruptly escarped on the west, but in 

 which the dip seems to be rather west than east, though, in the little outly- 

 ing limestone knob, called Pilot Rock, the beds have a well-defined dip of 

 20° to the south and east. All along both flanks of the northern portion 

 of the range, particularly on the Skull Valley side, are numerous springs, 

 some of fresh water carrying considerable lime, but many of them highly 

 charged with chloride of sodium. On the steeper chffs, the line of the old 

 lake-terraces is marked by a deposit of calcareous tufa. 



Islands. — Stansbury Island was formerly connected with the mainland 

 by a low beach-line, which is now in great measure covered with water. 

 The island itself is a rugged mountain-ridge, with precipitous slopes, which, 

 though only three miles in width at its greatest lateral extension, rises nearly 

 3,000 feet above the lake-level. It is formed mainly of beds of the Lower 

 Coal-Measure limestones, which form a sharp anticlinal fold, dipping 75° in 

 either direction, with a general north and south trend. These limestones 

 abound in corals, among which has been recognized: 



Zaphrentis Stansbury i. 



Zaphrentis multilamella. 

 From a black limestone near the top of the peak was also obtained: 



Euompkahis siibplanus. 

 Underlying this black limestone is a bed of about 200 feet of lighter- 

 colored siliceous rock. Along the flanks of the hills, especially on the 

 eastern shore, is a considerable development of light-colored beds, consist- 

 ing of sandstones and quartzites, which have been referred to the Weber 

 Quartzite, as at Black Rock Point, though they may only represent the 

 upper impure beds of the Wahsatch limestone. These beds are both 

 compact and heavily bedded, and thinly laminated. On the southern 

 portion of the eastern shore, they have a strike of north 18° east, showing 

 a tendency to close around and cover this end of the anticlinal. The upper 

 terrace-line on the island is marked by an abundant tufaceous deposit. In 

 general, the geological structure of the island seems to resemble that of the 

 Aqui Mountains, of which it forms a northern continuation en echelon, and 

 perhaps may have a similar faulting, which has thrown up the western side 

 of the fold. 



