The Pre-Jurassic Surface of Montana.

It has long been known that, prior to the deposition of Jurassic sediments, Montana was subjected to an intensive period of erosion. Mention of this may be found in numerous reports, especially those dealing with western Montana.

An Isopach Map and Discussion of the Marine Jurassic of Western United Sates and Canada

Recent demands for petroleum to carry on the war effort have resulted in widespread prospecting in the northern Great Plains. Nearly all oil wells now drilled are of a depth to penetrate the marine Jurassic formations. It is known that these strata differ in thickness from place to place, but information of distribution, thickness, and lithology has not yet been compiled.

An Isopach Map and Discussion of Triassic Strata in Southern Montana and Wyoming

Oil and gas have been found in the Triassic strata of Wyoming. Although the Triassic has not as yet proven to be a large producing horizon it is very probable that ad­ditional oil will be found in Triassic strata in the future, and it is one of the goals at which oil well drillers aim their tools.