September 21, 1906.] 



SCIENCE. 



367 



'upper part of the Portage' of the classi- 

 fication proposed by Williams in 1884 ; and 

 the name Enfield is applied for the name 

 of the town of Enfield where the member 

 is typically exposed. 



The boundary between the Nunda and 

 Chemung formations is established on the 

 basis of change in the generic composition 

 of the faunas occurring at the horizon indi- 

 cated. The two genera Dalmanella and 

 Douvillina, and the species Spirifer dis- 

 junctus are among the more character- 

 istic of the forms marking this change. 

 The Cayufa shale member contains the 

 typical Chemung fauna of the Chemung 

 Narrows section; it is paleontologically 

 limited by the Nunda fauna below, 

 and by the fourth of the known zones 

 of Tropidoleptus appearing above the 

 Hamilton formation, to which the name 

 Swartwood Tropidoleptus zone has been 

 applied by the author for the outcrop 

 southwest of Swartwood at an altitude of 

 about 1,600 feet A. T., containing the 

 fauna. 



The name Cayuta is applied for the 

 Cayuta Creek, along the sides of which 

 from Cayuta Lake to its discharge into the 

 Susquehanna River typical exposures of 

 the Cayuta member may be seen. 



The second member of the Chemung is 

 named Wellsburg sandstone member for its 

 outcrop at Wellsburg and above in the hills 

 of Ashland. It is paleontologically dis- 

 criminated by absence of many common 

 Chemung species and lithologically by the 

 more sandy nature of the rocks; and the 

 thin-bedded slabs characteristic of the 

 higher 'Catskill' rocks are conspicuous in 

 the upper portion. 



The Wellsburg member is terminated 

 above by the Fall Creek conglomerate 

 lentil, a thin band of conglomerate dis- 

 covered in place at the top of the Ashland 

 Hills and frequently visible in detached 



pieces on tops of other hills along the 

 southern townships of the state. 



The Fall Creek conglomerate lentil is 

 interpreted to be the equivalent of the con- 

 glomerate of that name in Bradford and 

 Tioga Counties, Pennsylvania. In the 

 beds immediately under the conglomerate, 

 and terminating the Wellsburg member, 

 occur in great abundance the shells of 

 Leptostrophia nervosa and Ortliothetes 

 chemungensis. To distinguish this partic- 

 ular horizon the name Ashland Leptostro- 

 phia zone has been applied to the zone by 

 the author. The author stated that other 

 evidence obtained by comparison of this 

 section with others indicates that the high- 

 est stratigraphic extension of the Chemung 

 fauna is not reached at the top of the 

 Wellsburg member, but that to the west 

 and south of this section rocks strati- 

 graphically still higher may bear many of 

 the species of the Chemung formations. 



Professor Williams's paper was discussed 

 by Messrs. J. C. Branner, C. A. Hartnagel 

 and D. S. Martin. 



Abyssal Igneous Injection as a Causal Con- 

 dition and as an Effect of Mountain 

 Building: Dr. R. A. Daly, International 

 Boundary Commission, Ottawa, Canada. 

 (Illustrated with a diagram.) 

 The contraction theory of mountain- 

 building is hypothetically extended to 

 cover the explanation of igneous intrusion, 

 geosynclinal down-warps, the location of 

 mountain-ranges, and the common associa- 

 tion of intense mountain-building with the 

 batholithic intrusion of magma. Among 

 the chief postulates are: (1) an earth-crust 

 about twenty-five miles thick, overlying a 

 substratum which, on account of its high 

 temperature, acts as a viscous liquid; (2) 

 the division of the crust into a shell of 

 compression about five miles thick, over- 

 lying a shell characterized by cooling ten- 

 sion. The shell of tension extends from 



