Page:Encyclopædia Britannica, Ninth Edition, v. 4.djvu/776

Rh 700 leaves the Sacramento and San Joaquin plains, and travels into the mountains, it becomes quite perceptibly warmer, at least for the first 2000 or 3000 feet of ascent. Thus, the mean temperature of the year at Colfax, 2400 feet above the sea-level, was, for 1871, 1 6, and for 1872, l - 4 higher than that of Sacramento, which is only 30 feet above the sea. As high up as 8000 or 10,000 feet the days in summer are comfortably warm, and even on the high peaks of the Sierra, at 12,000 or 13,000 feet of altitude, at mid-day it is usually so warm that an overcoat is not needed. At night, however, at these elevations, it is almost always so cold that frost occurs, although occasion ally it is very warm all night long, even at as great an altitude as 8000 feet. It adds very much to the pleasure of travelling in the High Sierra that the weather is, by day, almost all summer long, delightfully mild and clear, and without rain ; so that one of the greatest discomforts to which tourists are exposed in Switzerland and most other regions of pleasure-travel is here entirely unknown. Geology. The geological structure of California is com paratively simple, although the extreme paucity of fossils in the rocks of the gold region for a long time rendered it impossible to ascertain the age of the auriferous belt. It is also true that, for similar reasons, the formations which make up the main body of the Coast Ranges were not easily made out. A geological survey was authorized by the legislature in 1860, and continued, with occasional stop pages, until 1874. In the published volumes and maps which have been issued in the course of this work, almost all that is known with accuracy in regard to the geology and mineral resources of the State may be found. The Sierra Nevada first claims attention, as being the dominating range, It has a central core or axis of granitic rock, which forms almost the whole body of the range in its southern portion, diminishing in width as it is followed towards the north. All the higher points of the Sierra, in its most elevated portion, are of granite. Farther north there are a few high peaks of metamorphic rock, and many of the summits are capped with volcanic materials. Flank ing the granite is a very heavy mass of slaty metamorphic rocks, commonly known as the auriferous belt of the Sierra. This consists chiefly of argillaceous, chloritic, and talcose slates, with a great variety of other metamorphic rocks in smaller amounts, and some large, apparently isolated patches of limestone, which succeed one another in the line of direction of the axis of the range. The strike of the slates is usually parallel with that of the axis of the range, and their dip is, in general, at a high angle towards the east. Low down in the foot-hills, sandstones of Tertiary and Cretaceous age occur in considerable quantity. From the Stanislaus River towards the south, these strata are Tertiary, and they form qxiite a broad belt en White River and Pose Creek. On the American River, and north of it, the Cretaceous recks are occasionally well developed and full of organic remains. All these beds rest in almost horizontal position on the upturned edges of the aurifercv.s slates, showing that the elevation and metamorphism of the chain of the Sierra took place previous to the Cretaceous epoch. These beds are of marine origin; but there are very extensive masses of sedimentary materials higher up in the Sierra w r hich are fluviatile and fresh-water deposits, and they are associated with great quantities of volcanic detri tus and solid lava which has evidently ccnie down from the higher portions of the chain. The eruptive materials do not usually lie where they were ejected, but seem to have been carried far from their original position by cur rents of water, as they are made up, in great part, of rolled or brecciated masses, and are interstratificd with gravels and finely laminated clays. These latter often contain impressions of leaves and whole trrnks of trees, usuallv silicified, as well as bones of land and aquatic animals. The character of these fossil remains indicates that the formation is of late Tertiary age, and it may be considered as Pliocene. Although the crest of the Sierra is frequently crowned by large masses of volcanic materials, there are no indications of present activity along the range, and only occasionally can remains of ancient crateriform openings be seen. In Plumas County, however, and especially in the neighbourhood of Lassen s Peak, there are several sol- fa taric areas and well-formed cinder cones, some of which exhibit very marked appearances of recent action. From here northward, volcanic masses cover more and more of the higher regions, and almost the whole of the north-eastern corner of the State is exclusively occupied by rocks of this character. Lassen s Peak (10,577 feet) and Mount Shasta (14,440 feet) are both extinct volcanoes, and the latter has, near its summit, hot springs and indications of sol fataric action. The auriferous slates of the Sierra contain occasional fossils ; and, in quite a number of localities, these have been found in close proximity to well-marked and productive veins of quartz, which are now, or have formerly been, extensively worked for gold. These fossils are of Jurassic age, and no Silurian or Devonian forms have ever been discovered anywhere in the Sierra. In Plumas County, Triassic fossils have also been discovered, but only in one locality of limited extent. These are, however, identical with species belonging to the Alpine Trias, which have been found in large quantities, and in numerous localities, on the eastern sids of the Sierra, and which prove that this interesting group of rocks has a wide distribution on the Pacific side of the continent. The limestone belt, already mentioned, appears to be entirely destitute of organic remains, except in the extreme northern part of the State, where, in one or two localities, it has been found to contain well-marked carboniferous types. Farther south, this rock has become much metamorphosed, and is in many places converted into marble, while its organic remains appear to have become entirely obliterated. The Coast Ranges are made up almost entirely of Cre taceous and Tertiary marine strata, chiefly sandstones and highly bituminous shales. The Cretaceous rocks occur from the Canada de las Uvas northward along the east side of the Coast Ranges, gradually occupying more and more f-pace in a northerly direction. After passing the Bay of San Francisco, this formation makes up nearly the whole mass of the mountains, which grow more elevated and rougher towards the north, the rocks being much meta- moiphoscd and broken by granitic intrusions. In the vicinity cf Clear Lake (latitude 39) there is a belt of volcanic materials, accompanied by hot springs, and solfataric action, crossing the ranges from east to west. The Coast Range mountains have been much disturbed, and in part elevated during the most recent geological epoch, as large masses of strata of Pliocene age are found in various localities to have been turned up on edge ; but volcanic activity seems to have been more general and continued to a later date in the Sierra than in the Coast Ranges. Seme of the granitic masses along the shores of the Pacific are more recent than the Miocene Tertiary, as strata of this age have been uplifted and turned up on edge by the protruding granite. Indeed, everything in the Coast Ranges points to great geological disturbances as having occurred at a very recent date. Among the illustra tions of this condition of things, the changes produced by earthquakes in mcdcrn times may be cited. Like all the rest of the Pacific coast, California is liable to these disturbances, and this circumstance has undoxibtedly had considerable influence in retarding the settlement of the State. No year has been known, since the conquest of the ccuntiy by the Americai s, so disastrous as were the spring