rilVSlCAL AM) CMMATAL (OXDITIOXS. l^;; 



(|ue.stions is, iit wlml st !!<,'(' (tf eluvatioii or dcin'cssion was 

 it iir()(liK'('(l. Tlic s('('()ii(l is lliat wii imist iidt iiifni" tliat 

 ll)c i)liivati<tiis and dt^pressiniis were necessarily miil'oriu 

 locally, hut lliat tlu^y were diHereiit in amount in dillei-ent 

 jtlaces, and that elevation of mountainous rt\i,Mons often 

 coincided with depression of plains, and r/Vv irrsd The 

 ohservations of l'|»ham and Spencei- as to what has heen 

 termed " war|>in<,'" illustrate this, and it has lieiiii finally 

 estahlished hy the work of Dr. (1. M. Dawson on the 

 Cordilleran glacier of the west aln^ady noticed. 



It is not my ])urpose h(M'e to discuss the causes of the 

 elevations and d(q)ressions (tf the continents in the later 

 tertiary time. The attempt to account primarily for 

 depros.>ion or elevation of tiie land or the ocean level hy 

 the accumulation (tf ice on the land is futile, since that 

 accumulation itself must have dejtended lai'jjfely on the 

 c!ian<;es of elevation and of consecpient distrihution of 

 land and water. Primarily, the great elevation of the 

 land must have heen caused ity the slow depression of the 

 ocean bod in the intervals between those local foldings of 

 the crust wliich result from and relieve such depression. 

 That some later or secondary portion of the local did'eren- 

 tial depression of mountain regions may have been caused 

 by tlie great weight of ice heaped on them is probable; 

 but it is evident that this effect is cpiite inconsistent with 

 the idea of wide-H))read continental glaciers. 



Stutlents of glacial ])henomena are no doubt right in 

 directing attention to the great sensitivene-s of the crust 

 of the earth to jtressure. The ])henomena of river deltas 

 and of such great tliicknesses of sediment as those of the 

 coal-formation, shows, as I have elsewhere often argued, 

 that every foot of sediment placed on any part of the 

 earth's crust must produce a corresponding depression 



