proceedings: geological society 111 



The program of the 244th meeting, at the Cosmos Club, April 26, 

 1911, was as follows: 

 Notes on the geology of the Koyukuk-Kobuk region, Alaska. Philip 



S. Smith. 



There are two main physiographic features (Da high mountain mass 

 to the north known as the Endicott or Baird Mountains, which has been 

 correlated with the Rocky Mountain system in the States, and 

 irregularly distributed highlands and lowlands to the south, forming 

 what has been called the central plateau province. Roughly speaking, 

 the mountain province lies to the north of the Kobuk, and the central 

 plateau province to the south of that river. 



The geology of the Endicott Mountains is complex. Schists, lime- 

 stones, and intrusives, Paleozoic or older in age, are intruded by granu- 

 lar rocks, both granites and diorites, probably of Mesozoic age. Presum- 

 ably these mountains owe their main outlines to post-Cretaceous deform- 

 ation and it is possible that this period of mountain building may have 

 occurred well along in the Tertiary. The mountains have been eroded 

 by glacial as well as fluviatile agencies. 



The southern province consists mainly of deformed Cretaceous ami 

 older metamorphosed sedimentary rocks, the oldest of which have been 

 intruded by granular igneous rocks. In the lowlands Tertiary (?) lavas 

 have been extruded on the eroded surfaces of the older rocks and here 

 and there extensive deposits of gravel reaching to elevations of 500 to 

 600 feet above the main drainage lines probably represent deposits 

 formed during the waning of glaciation in the mountain province. 



One of the striking features of the region is the irregular arrangement 

 of the drainage. Certain of the larger streams flow transverse to the 

 ranges in rocky gorges. The valleys of these streams have been occupie* 1 

 by glaciers or were the spillways through which glacially impounded 

 drainage was discharged. 



A summary of the geologic history is as follows: The earliest recorded 

 event was the laying down of the sedimentary rocks of the Endicott 

 Mountains. These, after consolidation, were deformed and intruded 

 by basic igneous rocks and then intensely folded so that the rocks be- 

 came crystalline schists. 



After deformation, the region appears to have remained above the 

 sea until the laying down of the Mesozoic sediments. Into these rocks 

 and probably into the metamorphic rocks, granitic and dioritic intru- 

 sives were injected probably in middle Jurassic time. These intrusions 

 were followed by erosion and by the laying down of Cretaceous sedi- 

 ments. Subsequently these rocks were deformed although there was no 

 accompanying development of schistosity. During this period the 

 major outlines of the present topography were blocked out. 



A new system of Quaternary lakes in the central Mississippi. Basin. E. 



W. Shaw. 



Many of the low-lying parts of the central Mississippi Basm are under- 

 lain by a more or less laminated clay containing locally, especially about 



