310 proceedings: geological society 



the shale. Numerous anticlines heading in the central part of the 

 ranges on the west side of San Joaquin Valley, running out into and 

 plunging beneath that valley, form traps in which the oil has accumu- 

 lated and is now retained. Each of the productive fields on the west 

 side of the San Joaquin Valley shows all the features listed and the 

 intervening non-productive areas lack one or more of them. 



The sandy beds that form the reservoirs for the oil outcrop in or 

 near the fields. Escape of the oil is prevented by a sealing of these 

 beds by tar. This tar is the result either of the fractional distillation 

 of the oil and removal of the lighter constituents or of interaction of 

 oil and mineral waters, both probably being effective. Oil moving 

 upward through the sandy beds overlying the shales, being prevented 

 by this tarry seal from further movement, moves outward down the 

 dip through sandy beds lying stratigraphically above the bed resting 

 unconformably upon the shale. Oil moves through these upper beds 

 away from the plane of unconformity until its further movement is 

 prevented by a sealing of these upper beds by tar. The tarry seal 

 in this case may be formed, as in the case with the outcrop, by natural 

 fractionation of the oil, but in the deeper sands it is evidently caused 

 chiefly by the action of "edge water" on the oil. The tarrification of 

 oil in the presence of water is well recognized in the fields, and this 

 knowledge is of practical value in drilling for the deeper sands, since 

 it furnishes a guide as to the proximity of water. 



The productive sands, although occurring in a definite zone in the 

 lower part of the formation that rests upon the shale, are not con- 

 tinuous sands, but lie rather in a step-like arrangement, one small 

 oil sand above another, all of them abutting against the diatomaceous 

 shale on the flanks of the anticline, but diverging more and more widely 

 from the shale toward the axis of the syncline. 



Charles T. Lupton: Notes on the stratigraphic and structural 

 relations in southern and eastern Bighorn Basin, Wyoming. 



Bighorn Basin is a large topographic and structural depression in 

 northwest Wyoming nearly surrounded by Bighorn, Bridger, Owl 

 Creek, and Shoshone Mountains. It is drained by Bighorn River, 

 which flows through deep canyons in the mountain rim at the south 

 (Wind River Canyon) and at the northeast (Bighorn Canyon). 



The rocks exposed in the basin range from Cambrian to Quarternary 

 in age. Only those formations between the Morrison and the base 

 of the Wasatch were considered in detail. Leaves of Cretaceous age 

 were found during the field season of 1915 in the upper part of the 

 Morrison formation near Ten Sleep. The overlying Cloverly forma- 

 tion, Thermopolis and Mowry shale, Frontier formation, Cody shale, 

 Mesaverde formation, Bearpaw (?) shale, Lance (?) and Fort Union 

 formations were described in considerable detail. Of these, the Clover- 

 ly, Mowry, and Frontier produce a light, high grade oil and some gas. 

 The Cody shale is equivalent to the upper part of the Colorado and 

 the lower part of the Montana groups. The Mesaverde on the south 



