TITLES AND ABSTRACTS OF PAPERS 115 



out by saiul-plains. As for tho hypothesis of telling, if the streams on the west 

 were diverted into northeast courses and the seekock on the east side cuts a 

 northwest course, at right angles to the tirst described, he is left in doubt as 

 to the direction of the telling, regarded as a feature of continental extent. 



\'icc-Prosiilcnt II. K. (irc^iioiT took the cluiii-. 



(• i/.(7\.177(>V VOLCANOES 



nV \V 1 1,1.1 AM MKUr.KKT HOHns 



( Ahstidct ) 



The pai)er offered an exi)lanation of the manner of formation of such pecu- 

 liar craters as the volcanic Reis, the Steinheini crater, Coon Butte, and the 

 Zuni Salt Lake. This explanation is found in the peculiar properties of lime- 

 stone in contact with lavas under different pressures. 



l*rcsontO(l without notes. 



RELATIONS OF FAULT-BLOCK MOf STAINS TO FOLDED CHAINS 

 BV ,t. 15. WOODWORTII 



(Ahiitrart) 



The se<iuence of geological events in the mountain-luiilt tracts of North 

 America exhibits such dei)enden<e of fault-block moiuitains (or basin range 

 structure) on antecedent folded chains as to warrant th» statement that the 

 two contrasted types of geological structures are causally related in the 

 proldem of mountain-buihling. The structure of the Appalachian i)r()vince of 

 ea.stern North America, that of the Lake Superior region, and the geological 

 se<*tion from the Yellowstone Park westward across southwestern Montana 

 are appealed to as illustrating the schematic development in time and place 

 of mountain folds and subsequent normnl faulting. The place occupied by 

 dominantly acid intrusions in the episode of folding and of dominantly basic 

 erni>tives in the episode of faulting are pointed out, together with the position 

 of non-marine seclinients of the graywacke tyi)e associated with coal or vegetal 

 deposits in the evolution of the geological structure. The occurrence of red 

 \tei\s in the clo.sing .stages of faulting and otluM- corrcbitions are briefly stated, 

 iiiclndini: the iihue of nnconfoi-iiiitics ( pciu'plaiics i in the actual order. 



Presente«l without notes. 



Disrrssiox 



Prof. W. II. lIoi'.i'.>: I would sug'.rcst a sli;;Iit change in the us<» of terms 

 "underthrust" for '•ovcrthrust" and an abaiHloiiineiit of flic tciiii "tciisional 

 stres.s" in <-onnection with normal faulting. The mechanics of the folding 

 process indicate that th<' active for<-e in the cjis«> is from below an<l in fi-iin( 

 of a risin-.; an'if-linc. not Ironi above and behind. Soiie .\c'i*s sin-c. in a stinh- 



