More than a quarter of a century ago geologic exploration of the southern part of central Siberia was begun by geologists of several institutions, including the Central Geological Committee, which was joined later by a new geologic institution created during the Revolution—the West Siberian Branch of the Geological Committee. The members of this latter institution, commencing their explorations 12 years ago under the scientific direction of Prof. M. A. Ussov, have continued up to the present their intensive and productive work.
The present paper is based on the field data obtained during my extended explorations in the western half of the region under consideration and also on those assembled by other explorers during the same period.
The principal ideas presented in this report were published in general form1 15 years ago.
In developing these ideas, I published a second paper 2 in 1927. In the last few years . . .