When we consider the variety of different conditions prevailing in oil fields, it is evident that some sort of a classification is needed. In order to be of most practical service, this should be based on the most conspicuous distinguishing factors prevailing in a majority of the fields. What, then, is the most conspicuous type of phenomena displayed in an undeveloped oil field? Without doubt, it is the geological structure; hence we choose structure as the starting point in our classification, as we do in our detailed field investigations.
The structural factor has been realized for several decades by the exponents of the anticlinal theory, and in 19101 the structural classification was proposed as an offshoot of that theory. The purpose of this paper is to broaden the subject by discussing, first, the classification, and secondly the apparent exceptions. We might almost say that the knowledge of favorable structures is . . .