CHAPTER III. 



GEOLOGY OF THE WESTERN RANGE OF SIERRA NEVADA. 



RELATIONS OF WESTERN RANGE OF SIERRA NEVADA TO MOUNT SHASTA AND THE SIERRA NEVADA OF CALIFORNIA. GENERAL GEOLOGICAL 

 RELATIONS OF MOUNT SHASTA. COAST LINE ONCE FORMED IIY THE SIERKA NEVADA AND CASCADE MOUNTAINS SUCCESSIVE STAGES 



IX THE ELEVATION OF THE CONTINENT CONTINUITY OF THE COAST MOUNTAINS TRANSVERSE CHAINS. LlNES OF FRACTUKK 



DIVERGENT FROM MOUNT PITT AND MOUNT SHASTA, CARBONIFEROUS LIMESTONES OF MOUNT SHASTA, PERHAPS CONTINUOUS WITH TUB 



METAMORPH1C LIMESTONES OF THE SIERRA NEVADA LOCAL GEOLOGY. TRAP PLATEAUS ABOUT FORT READING. CoAL NEAR McCUM- 



BEK S FLAT. RECENT VOLCANIC ROCK AROUND THE BASE OF LASSEN S HUTTE LASSEN S BUTTE A VOLCANIC CONE. LAVA PLAIN ON 

 CANOE CREEK. CHIMNEYS SUBTERRANEAN GALLERIES TRAP PLATEAUS AT THE MOUTH OF CANOE CREEK. INFUSORIAL MARLS os 

 BANKS OF PIT RIVER. BEDS OF ROUNDED STONEB UNDERLYING MARL8. TRAP FORMING THE WALLS OF THE LOWER CANON OF PIT RIVER. 

 MOUNTAIN OF METAMORPHIC SLATE. 



FROM Fort Reading we passed southward of the limestone mountains mentioned in the last 

 chapter, and following a course little north of east, crossed that portion of the Sierra Nevada 

 which connects Lassen s butte with Mount Shasta ; coming down on to Pit river, at the upper 

 end of its long canon or series of canons, formed by its passage through this chain of mountains. 

 Some differences of opinion have prevailed in reference to the relations which this range sustains 

 to the Sierra Nevada on the one hand, and to Mount Shasta on the other ; but it has been 

 generally regarded as a spur of the Sierra Nevada running off at a considerable angle with the 

 main trend of that chain to connect with Mount Shasta. It has also been supposed that east 

 ward of Mount Shasta the main range of the Sierra Nevada would be found extending northward 

 and connecting directly with the Cascade mountains of Oregon. Mount Shasta has even been 

 claimed as a portion of the coast mountains, and is so represented by Dr. Trask, (GeoL Report, 

 1853, p. 48.) 



Dr. Trask also suggests that the Sierra Nevada terminates at Lassen s butte, and that the 

 coast mountains, when continued northward, form the Cascades of Oregon and Washington 

 Territories. 



Both these hypotheses seem to me untenable. So distinct a line of upheaval connects Mount 

 Shasta with Lassen s butte, and Lassen s butte with the Sierra Nevada, that they all seem to 

 form the inseparable parts of a single mountain system. 



As has before been stated, the geological data are still wanting for determining with precision 

 the relative ages of the Sierra Nevada and coast mountains ; but the evidence, as far as it goes, 

 is altogether in favor of the greater antiquity of the Sierra Nevada, and of the connection of 

 Mount Shasta with the older system. The most characteristic fossiliferous strata of the coast 

 mountains have not yet been found in the Sierra Nevada. 



The physical structure of the country traversed by these mountains teaches the same lesson. 

 The Sierra Nevada, including Lassen s butte and Mount Shasta, form the wall which bounds 

 the elevated plateau. The eastern bases of these mountains are four thousand feet above the 

 western, and it seems difficult to resist the conclusion that at one stage in the elevation of the 

 continent the mountains I have mentioned, with the Cascades of Oregon, formed its western 



