PROCEEDINGS: GEOLOGICAL SOCIETY 297 



liquid or solid explosive; and the fact that the force of a detonated ex- 

 plosion is often in the direction of the detonating impulse and inde- 

 pendent of the configuration of surrounding materials (Pel^e, Lassen); 

 are all applicable to the explanation of known phenomena of volcanic 

 explosions. 



E. O. Ulrich: Newly discovered instances of early Paleozoic 

 oscillations. Anyone who will undertake a comprehensive course of 

 critical and detailed comparison of stratigraphic sections must inevitably 

 reach the conclusion that the old land surface was exceedingly unstable 

 with respect to sea level and subject to oft-repeated differential move- 

 ments and warping. 



At times certain parts were pushed up, while other parts lagged, and 

 yet others sank, actually or but relatively, beneath sea level. In other 

 words, the vertical movements of the lithosphere were differential, 

 and the displacements of the strandline were not erestatic, as taught 

 by Suess, but varied in volume and direction from place to place. 



The differential character of the movements of the continental areas 

 with respect to sea level is indicated by abrupt local, or even widely 

 distributed changes in the character of the sediments; by imperfections 

 in the record of marine deposits at one place which are partly and some- 

 times, perhaps, wholly supplied in the sedimentary record at another 

 place; by the sudden extinction of, say, an Atlantic fauna in a given 

 area by a Gulf of Mexico or an Arctic fauna; and by other more or less 

 competent criteria. 



Most convincing evidence of land tilting, with alternating east and 

 west tilts more common than those to the south or north, was brought 

 out by detailed comparisons of the sedimentary record on the flanks of 

 old uplifts in interior North America. Particularly illuminating are 

 the facts showing restriction of formations of considerable thickness 

 to one side of such uplifts and similar restriction of other formations to 

 the opposite side. Geographic restriction of deposits, hence also of 

 the seas in which they were laid down, is indicated over and over again 

 on the flanks of the Cincinnati, Nashville, Ozark, Wisconsin, and 

 Adirondacks domes. These domelike areas rarely, if ever, formed 

 islands. As a rule, when they were not completely submerged, they 

 were connected with larger land areas, often probably forming penin- 

 sular projections. 



Oscillation of land and sea areas was the rule also in the Paleozoic 

 Appalachian Valley. However, the conditions here dift'ered in that the 

 seas were largely confined to subparallel structural troughs. These 

 troughs were not all submerged at the same time; and only very seldom 

 was any one of the five or six troughs submerged throughout its length. 

 As a rule tilting, or difi"erential movements, produced canoe-like de- 

 pressions which, when they reached depths permitting marine submer- 

 gence, formed narrow inland bays. These bays were emptied and again 

 filled many times, and each submergence differed more or less in its 

 geographic expression from those preceding it. 



