Congressional Edition Volume 5243 (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. 1907 Excerpt: ... the river, at the old lock site south of Bohio and east of Pena Blanca, quite a different phase of this formation is exposed; it consists of alternating layers of sandstones and course conglomerates all clearly water transported and deposited. Many of the bowlders are a foot or more in diameter; they are of andesites for the most part, but not a few are of a lighter colored porphyritic rock with abundant hornblende crystals. The finer layers and the cementing material are very like the rock occurring at the Bohio quarries. Crossbedding is common and fine material often occurs in lenses in the grits and conglomerates. The prevailing strike is N. 25 E., and the dip to the northwest at an angle of about 14 degrees. The identity of these conglomerates and the more even-textured breccia-like rock is not at all evident in the field, but many borings made in the vicinity show a gradual transition southward from the even-textured breccias of Bohio to the conglomeratic facies at Pena Blanca. The boring made at kilometer 24 (hole 24-b) is of interest, since it shows carbonaceous sandstones in the middle part and fossils in the lower part of the core. Further study of this formation to the southeast and by means of borings has shown that it is of variable character, in some places clearly sedimentary and water sorted, both fine grained and conglomeratic; in other places the appearance is more that of a volcanic breccia, possibly water laid but not water transported. The pyroclastic appearance may be a deceptive one and due to the alteration of the rock. In general the formation may be described as a probable fluviatile deposit characterized by sudden changes and transitions, the composition of the materials being fairly uniform. It is not improbable that volcanic eru...