Abstract

Introduction.

In previous papers the writer has endeavored to show the changes taking place in the preliminary stages of rock-weathering as illustrated in the post-Cretaceous and post-Glacial disintegration of the granites of the District of Columbia and the diabase of Medford, Massachusetts.* The purpose of the present paper is to discuss the results of similar processes, operating for longer periods, and incidentally to refer to other matters with which the subject is closely affiliated.

The material selected for investigation is a highly micaceous, feldsparrich gneissoid rock and its residual clay, occurring at North Garden, in Albemarle county, Virginia. The region lies to the west of the Cretaceous submergence, the accumulated gravels of which enabled us to set an approximate time limit to the weathering manifested in the District of Columbia rocks, and thus no criteria are afforded for estimating the relative rapidity of the process. The amount of material lost through leaching and

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