PT. 1. Geology. PT. 2. Paleontology Volume 1, PT. 2 (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1858 Excerpt: ...Grand rivers (or rather the upper brandies of rivers which bear those names in, and drain a part of the State of Missouri), both rise and run for the first twenty-five or thirty miles of their courses upon the Drift Deposit alone. The first strata that are expose'd by the deepening valleys of both these streams belong to the Upper coal-measures, and they both continue upon the same formation until they make their exit from the State, near the boundary of which they have passed nearly or quite through the whole thickness of that formation down to the top of the Middle eoal-measiires. Therefore, as might be expected, both these streams are very similar in their general characters so far as their Iowa portions are concerned. Their valleys are usually pretty well defined; but sometimes the surrounding high land slopes for a mile or more gently towards the stream. They gradually deepen from their upper portions downward, so that within fifteen or twenty miles, they have reached a depth of near a hundred and fifty feet below the general level of the adjacent high land, which depth they retain with little increase until they pass beyond the limits of the State, because the general slope of the country is nearly concurrent with the slope.of the streams. The strata of the Upper coal-measures consist, in this part of the State, of beds of limestone alternating with those of clayey and shaly composition. The latter readily soften and disintegrate upon exposure to atmospheric influence and the action of the streams. Thus when the rivers have cut their valleys down through the series of limestone strata, they reach those of clayey composition before mentioned. Upon these they widen their valleys and make for themselves broad flood-plains which become conspicuous feature...