The purpose of this paper is to present a discussion of the nature and origin of shaly structure and its relations to petroleum, together with brief reference to such observational and experimental data as seem pertinent to these problems.

In view of the paucity of knowledge and the importance of this structure from both scientific and practical points of view, the necessity for more extended, and particularly for more critical, field observations and for experimentation under more rigid control, is strongly urged. In the meantime, however, certain, tentative conclusions seem to be warranted, and these are set forth here in the hope that they may elicit discussion and thus aid in mapping out the most profitable lines of research.

Nature of Clay

Clay, which may tentatively be regarded as the chief antecedent of shale, has been defined2 as:

“A natural substance or soft rock which, when finely ground . . .

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