350 abstracts: geology 



The Birch Creek schists (pre-Ordovician?), the oldest rocks, occur in 

 the northeastern part of the area and are separated by a fault from a 

 series of quartzite tuffs and limestones lying to the south. The lime- 

 stones carry Carboniferous (Mississippian?) fossils. A series of green- 

 stones and schists occurring in the southernmost belt of foot-hills are 

 assigned to pre-Carboniferous age. The Mesozoic is represented by 

 basaltic lava flows and tuffs, with some shale (Triassic?), limestones 

 (Triassic), by slate, tuffs, arkoses, etc. (Triassic), locally highly meta- 

 morphosed, and by very extensive intrusions of diorite (Jurassic?). 

 There are also some areas of shales, with- coal-beds, conglomerate and 

 gravels, assigned to the Kenai (Upper Eocene). The Quaternary is 

 represented by the high gravels, sands, and silts which make up the pla- 

 teau, and by terrace deposits, both assigned to the Pleistocene, and by 

 the alluvium of the present water courses. All of these rocks strike 

 approximately east and west, and the prevailing dips are to the south. 

 Some evidence was obtained of extensive faulting. 



The gold placers of the region are in part reconcentrations from the 

 auriferous gravels of old Quaternary deposits. It appears that the bed- 

 rock source of the gold is in the altered phases of the Triassic slates, and 

 the mineralization is probably due to the influence of the dioritic intru- 

 sions. F. H. M. 



GEOLOGY.— The New Madrid earthquake. Myron L. Fuller. Bul- 

 letin U. S. Geological Survey No. 494. 1912. Pp. 119, with maps, 

 views and sections. 

 The succession of shocks designated collectively the New Madrid 

 earthquake occurred in an area of the central Mississippi Valley including 

 southeastern Missouri, northeastern Arkansas, and western Kentucky 

 and Tennessee. Beginning December 16, 1811,- and lasting more than 

 a year, these shocks have not been surpassed or even equaled for num- 

 ber, continuance of disturbance, area affected, and severity by the more 

 recent and better-known earthquakes at Charleston and San Francisco. 

 The earthquakes began a little after 2 a.m. on December 16 and con- 

 tinued the next day at short intervals, but gradually diminished in inten- 

 sity. They occurred at long intervals until January 23, when there was 

 another shock, similar in intensity and destructiveness to the first. 

 This shock was followed by about two weeks of quiescence, but on Febru- 

 ary 7 there were several alarming and destructive shocks, the last equal- 

 ing or surpassing any previous disturbance, and for several days the 

 earth was in a nearly constant tremor. 



