678 LG: CLAM IB TERTETIN, 
disappeared. This seems to correspond with the observed oscil- 
lation of glaciation in both Europe and America.* 
INTERCURRENT AGENCIES 
Without question the normal series of glacial oscillations 
just postulated would be subject to intercurrent influences which 
would be liable to disturb, perhaps quite seriously, its regularity 
and symmetry. 
1. Any notable movement in the land which affected the sum 
total of the atmospheric contact area would disturb the sym- 
metry of the series. 
2. Any notable change in the original supply of carbonic 
acid through volcanic action or other agency would produce 
obvious modifications. The deformation of the body of the 
earth out of which the conditions of glaciation are assumed to 
have sprung would doubtless be favorable to volcanic action, and 
if this reached a degree of intensity sufficient to add appreciably 
to the carbon dioxide of the atmosphere, it would radically 
affect the ongoing of the process. That there was extensive 
vulcanism nearly or quite concurrent with glacial action has been 
urged by some geologists; indeed, glaciation has even been 
attributed to volcanic action. 
3. The precession of the equinoxes has been regarded by 
many thoughtful students of glaciation as an influential agency. 
If affective, it would superpose a rhythm of its own upon the 
rhythm postulated by this atmospheric hypothesis. For specific 
illustration the extensive series of moraines which marked the 
later stages of the Wisconsin epoch of glaciation are referred by 
Taylor to precessional influence, while the Wisconsin glaciation 
itself would, under the atmospheric hypothesis, be referable to 
atmospheric depletion. The most serious question which here 
arises is the compatability of the prolonged period implied by 
Taylor’s interpretation with the rate of reaction implied by the 
«The Classification of European Glacial Deposits, Jour. GEou., Vol. III, No. 3, 
pp. 241-269, JAMES GEIKIE; The Classification of American Glacial Deposits, zdzd., 
pp. 270-277, 1. C. CHAMBERLIN; editorial, zdz¢., Vol. IV, No. 7, October-November 
1896, pp. 873-876. 
