92 Basalts

The Geology and Petrography of Crater Lake National Park, 1902



As will be seen by consulting the map the basalts of Crater Lake comprise only the later volcanic eruptive masses that form the various cones, mounds, and flatter lava sheets to the north, west, and south of the lake. No basalts whatever are found in the walls of the crater or in the dikes cutting them. Nor are they to be seen on the immediate outer slope of the crater.

In the great majority of cases the basalts bear a very close resemblance to many of the andesites, and sometimes can not surely be distinguished as basalts. In not a few cases, however, typically developed basaltic structures are to be noted. This type will be considered first.

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