86 bulletin: museltm of comparative zoology. 



existence of glaciers demonstrate the wide distribution of the cHniatic 

 conditions producing Permian glaciation and where the traces of ice- 

 action exist in horizons below the Permian show that the glaciation 

 of that period was induced by causes not suddenly brought into play. 



In North America in latitude 42° S., Messrs. R. \V. Sayles and L. A. 

 Laforge have called attention to a remarkable breccia at the top of the 

 Roxbury conglomerate south of Boston in which many of the peculiari- 

 ties of glacial till occur, including a few striated pebbles. The precise 

 position in the time scale of this bed is not known from contained 

 fossils in the local series but its relations to the Narragansett coal 

 field on the south make it presumable that the beds are Permian. 

 In Oklahoma in about latitude 35° S. erratic blocks occur in a shale 

 of Subcarboniferous age. The striae on these transported stones 

 are of post-depositional origin due to rock motion but the transporta- 

 tion of the boulders remains unexplained except by floating ice. 

 The evidence from North America, as yet meagre, points to the same 

 conclusion as that derived from the distribution of breccias and 

 conglomerates of Carboniferous and Permian age in Europe. So far 

 as the facts from North America go, local glaciers are the most that 

 at present can be postulated. 



What combination of geographic with atmospheric conditions 

 brought about Permian or even Pleistocene glaciation we do not know 

 with any degree of certainty. All our hypotheses of glaciation 

 postulate glaciers and ice-sheets engendered from the fall of snow. 

 It is possible, though not now seemingly probable, that under the 

 peculiar recurrence of hailstorms which are, in the existing regime 

 unusual forms of precipitation, masses of ice might accumulate in 

 tropical and subtropical areas where snow never falls. 



Hail and allied forms of frozen rain-drops enter more largely into 

 glaciers in existing mountains than is perhaps commonly recognized. 

 Kaemtz (1845, p. 380-382) gives several citations to show- that hail 

 frequently falls on the Swiss Alps. It is probable that no small 

 amount of hail enters into the structure of Swiss glaciers. De Saus- 

 sure states that during a stay of thirteen days on the Col de Geant at 

 an elevation of 3,428 meters he was struck with the frequency of hail 

 and sleet which he observed eleven times. Balmont experienced a 

 shower of hail during the night that he passed on the summit of Mont 

 Blanc and Paccard found much hail beneath the snow with which the 

 summit is covered. 



Edward Whymper (1892, p. 164 ct seq.) describes frequent falls of 

 hail within the region of glaciers on the mountains of Ecuador. When 



