AKCH^AN ISLANDS. 425 



Islands. — The Archaean uplift of the Promontory Range is continued 

 to the southwest in the rocky summits, which lie above the level of the 

 lake, forming- Fremont and Antelope Islands, A small outcrop of Archaean 

 gneisses is also found rising out of the mud plain at the Landing-rocks, to 

 the west of Ogden, forming the extreme western point of the lake-shore line. 

 Fremont's Island is made up of beds of dark-green hornblendic and mica- 

 ceous gneisses, generally much contorted, in which the prevailing dip is 

 about 40° to the west, but on the western shore presenting a bold escarpment 

 toward the lake. The old terrace-lines are very distinctly marked, as upon 

 most of the islands of the lake. Antelope or Church Island, as it is some- 

 times called, is the largest of the rocky islands which dot the surface of Salt 

 Lake, covering a superficial area of about 40 square miles. It has several 

 fresh springs, and its slopes are covered with a good deal of grass, which 

 have been used as common grazing-ground for the herds of sheep and cattle 

 of the Mormon settlers. As seen from the shores of the lake near Farming- 

 ton, in profile, the crest of the southern portion of the ridge is a perfectly 

 horizontal line, evidently marking the level of one of the old lake-terraces. 

 It is made up entirely of rocks of the Archaean series, mostly gneisses, with 

 some quartzites and mica-slates. On the main peak is a thin stratum of 

 not more than 20 feet of slates, which approach a limestone in composition 

 These are the only calcareous beds that have been detected in the Archaean 

 rocks of the Wahsatch Range. They stand in an almost vertical position, with 

 a strike of north 45° west, and are enclosed on either side in gneissic rocks, 

 which form the main ridge to the south with the same strike. An outlying 

 spur to the west of the main ridge shows a secondary fold, whose axis has 

 an easterly and westerly direction, the beds dipping over 70° to the south. 



Curlew Valley. — To the wiBst of the Promontory Mountains, the 

 Rozel Hills and the southern end of the Hansel Mountains consist, as has 

 been seen, of low, flat tables of dark, compact basalt, forming part, doubt- 

 less, of the same flow now separated by the Quaternary deposits of the 

 valleys. To the west of the Hansel Mountains, the country north of the 

 lake, as far as the Terrace Mountains, appears to be underlaid also by the 

 basaltic formation, the southern extremity of the great outflow of basalt which 

 covers an immense area to the north of the limits of the map. Much of 

 the country here shown upon the map lies below the level of the upper 



