abstracts: geology 37 



formations in the area include the Pierre, Fox Hills, Lance, Fort Union, 

 White River, and Arikaree. The Lance is subdivided into three 

 members: a lower undifferentiated portion, 425 feet thick; a middle or 

 Ludlow lignite-bearing portion, 350 feet thick at most; and an upper 

 marine member, the Cannonball, 225 feet thick. 



The marine fauna of the Cannonball member is very similar to but 

 not identical with the fauna of the Fox Hills, which is of recognized 

 Cretaceous age, while the flora of the Ludlow lignitic member is so 

 much like that of the Fort Union, which is of recognized Tertiary age, 

 that it is impossible to differentiate it from the Fort Union on the 

 basis of the fossil leaves. 



Lignite beds are found in both the Lance and Fort Union formations, 

 the more important beds occurring in the Lance formation. 



D. E. W. 



GEOLOGY. — Reconnaissance of the Conconully and Ruby mining 

 districts, Washington. E. L. Jones, Jr. U. S. Geological Sur- 

 vey Bulletin 640-B. Pp. i-iv, 11-36, with 1 plate. 1916. 



This report describes the geology and ore deposits of a small area 

 in the central part of Okanogan County, Washington. In general the 

 rocks comprise an older series of metamorphic rocks and a younger 

 series of igneous rocks of batholithic origin. The metamorphic rocks 

 consist of schists, quartzites, and limestones. Some of the schists 

 are fine-grained and thinly laminated, but others are coarsely banded 

 micaceous rocks that are evidently altered sandstones. The most 

 schistose and gneissoid rocks are those which border the batholith. 

 Closely associated with this sedimentary series are dike rocks and lavas 

 that have undergone the same metamorphism and are probably of the 

 same age, which is supposed to be Carboniferous. 



The common igneous rock of the area is a gray granite which has 

 intruded the sedimentary rocks. It occurs over a large area and is 

 probably a part of the Similkameen batholith. There are other igneous 

 rocks of considerable areal extent, including a dark granite and an altered 

 green porphyry. Dikes are abundant, particularly along the contact 

 of the batholith with the metamorphic rocks; they include granite, 

 diorite, pegmatite, and aplite, and probably represent the closing stage 

 of igneous activity. 



The ore deposits are principally of two types, quartz veins and 

 disseminated or replacement deposits. The quartz veins are widely 

 distributed throughout the area, but those of proved value are grouped 



