INTERIOR VALLEYS. 417 



graphical resemblance, though their connection with well-defined Cambrian 

 strata has not been clearly traced out. 



Interior Valleys. — Of the great mountain-valleys which lie between 

 the two crests of the northern portion of the Wahsatch Range, Cache Valley 

 is the largest and most important. It occupies the great synclinal fold in 

 the Wahsatch limestone already mentioned, and is overlaid by horizontal 

 Tertiary beds of Pliocene age. They have been referred to the Humboldt 

 Pliocene formation, inasmuch as they are probably of the same age as the 

 beds which characterize such wide areas in the region of the Humboldt 

 Valley in Nevada. They cover the greater portion of the southern end of 

 the valley, except the broad fluviatile bottoms of the larger streams, and 

 rest unconformably against the inclined strata of the Wahsatch limestone 

 on all sides of the valley. The drainage-channels on the west side and to 

 the south, in the region of Saw Mill Canon, cut through the Tertiary, offer- 

 ing good exposures of a thickness at least of 350 feet of sandstones and 

 lime^stones. The upper beds are friable sandstone, which weathers readily. 

 A specimen subjected to chemical analysis yielded 94.44 per cent, of silica, 

 the residue being chiefly iron and alumina, with considerable moisture. 

 Below the red sandstones are found a series of fine-grained white and 

 lavender-colored sands, interstratified with layers of calcareous sandstones 

 Near Wellsville occurs a body of soft compact sandstone, which is used 

 as a building-stone by the inhabitants of the valley, as it is easily quarried 

 and cut without difficulty. Other quarries have also been opened; and, 

 from one near Mendon, a light porous rock was obtained, also much used 

 in building. The beds of Mendon yielded a number of fresh-water shells, 

 among which the genera Helix and Limncea are well represented. Prof. 

 F. B. Meek has described in his report a new species of the latter genus, 

 found at Mendon, as Limncea Kingii. In many localities, the Tertiary beds, 

 especially among the steeper western foot-hills, are concealed by deposits 

 of sand and coarse gravel, which belong to the Quaternary period. The 

 terraced benches, which are so marked a feature on the western face of 

 the Wahsatch, are also found along the foot-hills on both sides of Cache 

 Valley, although not so broad as those observed in Salt Lake Valley. 

 The entire southern portion of the former valley shows unmistakable signs 

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