PDF - Wallace Online

444 TROPICAL NATUREsurrounding plain or valley.What was once a single lavastream now forms several detached hills, the tops of whichcan be seen to form parts of one gently inclined plane, thesurface of the originallava flow, now 1000 feet or moreabove the adjacent valleys.The American and Yuba valleyshave been lowered from 800 to 1500 feet, while the Stanislausriver gorge has cut through one of these basalt-coveredhills to the depth of 1500 feet.While travelling by stage, in the summer of 1887, fromStockton to the Yosemite valley, I passed through this verydistrict, and was greatly impressed by the indications ofvast change in the surface of the country since the streams oflava flowed down the valleys. In the Stanislaus valley thenumerous " table mountains " were very picturesque, oftenrunning out into castellated headlands or exhibiting longranges of rugged black cliffs. At one spot the road passedthrough the ancient river-bed, clearly marked by its gravel,pebbles, and sand, but now about three or four hundred feetabove the present river. We also often saw rock surfaces ofmetamorphic slates far above the present river-bed, thusproving that the original bed-rocks of the valley, as well as thelava and gravels, have been cut away to a considerable depthsince the epoch of the lava flows. The ranges of " tablemountains," now separated by deep valleys more than 1000feet below them, could easily be seen, by their perfect agreementof slope and level, to have once formed part of anenormous lava stream spread over a continuous surface ofgravel and rockFossil Remains under the Ancient Lava BedsThese great changes in the physical conditions and in thesurface features of the country alone imply a great lapse oftime, but they are enforced and rendered even more apparentby the proofs of change in the flora and fauna afforded by thefossils, which occur in some abundance both in the gravels andvolcanic clays. The animal remains found beneath the basalticcap are very numerous, and are all of extinct species. Theybelong to the genera rhinoceros, elotherium, felis, canis, bos,tapirus, hipparion, equus, elephas, mastodon, and auchenia, andform an assemblage entirely distinct from those that now