The modern lake sediments and those of post-Provo age immediately preceding the present Great Salt Lake have about the same clay-mineral composition. In these deposits, the montmorillonite shows a relatively poor organization which may be a consequence of the presence of considerable sodium. The montmorillonite may be either detrital or precipated or formed by alteration of volcanic ash.

The illite, probably detrital, is generally well organized showing only a very small amount of degrading. The presence of kaolinite in all the lake samples is noteworthy. It is almost certainly detrital. There is a general absence of substantial mixed-layer components as well as of any chlorite, and there is no suggestion of attapulgite-sepiolite clay minerals.

The Alpine and Provo sediments of the Lake Bonneville terraces have a clay-mineral composition somewhat different from that of the modern lake sediments; they show a highly degraded chlorite and a very well-ordered montmorillonite.

The green clays of Early Pleistocene age also have a distinctive clay-mineral composition corresponding to a high content of illite and a low content of montmorillonite associated with the presence of chlorite.

The clays occurring in the Great Salt Lake Desert west of Knolls contain at a depth of about a foot a thin bed of nearly pure, unconsolidated dolomite.

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