90 bulletin: museum of comparative zoology. 



In the Northern Hemisphere on the existing shores of the Atlantic 

 Ocean glaciated stones are found entering into the contemporaneous 

 marine deposits much farther equatorward than those produced by 

 the action of coast-ice and the same extension is true for the occurrence 

 of glaciated ledges. Thus on the Atlantic coast of North America 

 glaciated ledges and deposits of true glacial till line the shore of the 

 United States as far south as New' York Narrows in latitude 40° 30' 

 north; no modern observer has described stones or ledges bearing 

 distinct traces of coast-ice action within this belt south of the British 

 possessions, though it is to be acknowledged that thin sheets of coast- 

 ice form in winter and may do some geological work of this character. 

 The reason for this greater equatorward extent of glacier-ice as con- 

 trasted with ordinary sea-ice is due to the extent to which glacier-ice 

 may be pushed equatorward beyond the gathering ground of the 

 glaciers. In a like manner, glaciers originating on high lands in low 

 latitudes may reach the sea-level and impress that region with marks 

 of glaciation where the normal sea-level temperatures at the time 

 preclude the existence of coast-ice. It can not be too much insisted 

 upon, therefore, that glaciation is of all forms of ice-action that most 

 likely to be met with in any marked degree at sea-level in low latitudes. 

 Hence it is the more reasonable to assume that the Permian ice-deposits 

 represent the existence of glaciers in the regions where these coarse 

 accumulations occur, invoking as we may where the geologic evidence 

 is permissible a favorable geographical relief such as now controls the 

 distribution of glacial ice at one place or another on the earth's 

 surface. 



The role which hail might play in producing glaciers in subtropical 

 regions as a complement to snowfall in higher latitudes and high 

 altitudes" is tentatively suggested as a factor in Permian glaciation, 

 but the feasibility of the thesis encounters some of the same objections 

 which meet the accepted origin of glaciers in snowfall. 



There are accumulating evidences of the existence of glaciation in 

 the Northern Hemisphere in Permian time, and there are not wanting 

 signs of ice-action, probably floating ice, in the preceding Carbonifer- 

 ous epoch, facts which assist in the attempt to devise hypotheses. 



The tendency of the geologic evidence is towards the recognition of 

 glacial conditions independent of latitude which points to a weak- 

 ness of the climatic zones, a feature characteristic of Palaeozoic 

 temperatures, in which non-glacial climates show no zones correspond- 

 ing to the present ones. 



The hypothesis of internal heat controlling surface temperature 



