. Elements of geology : a text-book for colleges and for the general reader. Geology. 16 AQUEOUS AGENCIES. larged and deepened by water and by ice. But there are some, at least, which may be proved to have been produced wholly by erosion, and that during the present or at least during very recent geological times. We refer especially to those which have been cut through lava-streams. In Middle and Northern California are found lava-streams which have flowed from the crest of the Sierra. By means of the strata on which they lie, these streams are known to have flowed after the end of the Tertia
. Elements of geology : a text-book for colleges and for the general reader. Geology. 16 AQUEOUS AGENCIES. larged and deepened by water and by ice. But there are some, at least, which may be proved to have been produced wholly by erosion, and that during the present or at least during very recent geological times. We refer especially to those which have been cut through lava-streams. In Middle and Northern California are found lava-streams which have flowed from the crest of the Sierra. By means of the strata on which they lie, these streams are known to have flowed after the end of the Tertiary period. Yet the present rivers have since that time cut. Fig. 8.—Lava-Stream cut through by Rivers: a a, Basalt; b b. Volcanic Ashes; c c, Tertiary; d d, Cretaceous Rocks. (From Whitney.) great canons through the lava and into the underlying rock, in some cases at least 2,000 feet deep. Such facts impress us with the immen- sity of geological times. This important point is discussed more fully in a subsequent part of this Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original LeConte, Joseph, 1823-1901. New York : D. Appleton and Co.
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