September-October 1878, Notes of Travel on the East Side of the Sierra Image 6

Creator

John Muir

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Transcription

8

Glaciation of Lava regions

Many of the lavas are so soft as to crumble under glacial action or so [cut] by clvg [cleavage] planes as to give way & break up in very irregular forms leaving a rough surface wh soon parts with glacial marking by subsequent weathering. The extreme variability also of the lavas both in the resistance offered to ice action & in the method of their acquirements of form greatly increases the difficulty of reading glacial history inscribed upon them. Sufficient however is [clear] to determine the fact that almost the entire lava deposits of the Sierra [covering] half the range in thick blankets & obliterating the pre-volcanic [Sierra] landscapes by filling its valleys & burying its hills & ridges & mtns [mountains] is pre glacial in age & that the greatest & most

9

universal of the later floods of fire were outpoured just at the period of the obliteration of the ancient rivers. Also there are hard lavas still manifesting the polish scratching & [moutoned/montanced] forms of glaciers together with well [defined] [moraines] in some favored places. Notably at the head of Independence Lake showing that the crumbled hills & hollows of this region with their various lavas sculptured into all kinds of fantastic & picturesque forms remain to this day almost unchanged however great the changes of the preglac periods & nowhere are these changes more strikingly exhibited on the very summit of the range along the head of the Feather tributary. There seems to have been a great val now filled with

Date Original

1878

Source

Original journal dimensions: 10 x 17 cm.

Resource Identifier

MuirReel25Journal06P008-009.tif

Publisher

Holt-Atherton Special Collections, University of the Pacific Library

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