TWENTY-SEVENTH ANNUAL MEETING. 225 



the direction of least resistance, which is over the continents. The warm 

 oceanic currents prevent the ice from reaching very far to the south in either 

 ocean. But there is nothing to prevent the ice from reaching very far to the 

 south in the region of Hudson bay and westward of that. 



NECESSITIES OF AN ICE PERIOD. 



Two features necessary to the accumulation of a large amount of ice are 

 the contiguity of large bodies of water and an increase in the summer heat. 

 These were obtained in the Gulf of Mexico, which in past times reached far- 

 ther north than at the present day, and the short hot summers that occur 

 during the platonic winter. Large quantities of water were raised from the 

 Gulf of Mexico and carried northward by the south winds until the ice was 

 reached, where it became quickly converted into snow or rain. Then, too, 

 the melting of the ice in the summer season furnished plenty of water close to 

 the ice; so that a three-day blow from the south could carry much moisture 

 far to the north. 



The north winds blowing over the ice fields had a temperature far below 

 freezing; and, supposing that changes in direction of wind occur as they do 

 at the present day, they would present this feature: A very warm south 

 wind heavily laden with moisture, met by a very cold north wind, causing pre- 

 cipitation of a large amount of moisture in the form of heavy snows in the 

 region of Hudson bay, and heavy rainfall on the plains south. Thus the 

 snow accumulated and was piled up higher and higher. This snow, by reason 

 of its great height and pressure, became packed solidly into ice and did as 

 glaciers always do, pushed its foot away from the region of greatest accumu- 

 lation toward the warmer regions. Hence it was pushed to the south until 

 the melting power of the sun exceeded the rate of travel of the ice. 



RATE OF TRANSIT. 



As to the length of time required to bring these rocks here. It is by no 

 means necessary to consider that they -should be brought from Ontario to 

 Kansas during a single epoch. These stones, you will observe, are a very 

 enduring kind. Indeed they seem even to become harder by exposure to our 

 southern sun; and, as Doctor Smith and I noticed in examining them, they 

 are mostly polished on the southwest side, apparently by attrition of the dust 

 particles raised during the few dust storms tliat we have. It is a higher polish 

 than is received by abrasion during transit. If they have been here long 

 enough to become so highly polished by so infinitesimal a cause, they have 

 been here long enough for all accompanying softer rocks, except in the 

 buried portions of the moraine, to have become entirely disintegrated and 

 carried away. Indeed, they have been here long enough for some of these 

 granitoid rocks to have become decomposed since their arrival, as is shown 

 by this specimen which I dug up from the buried portion of the moraine, 

 which, when I found it six weeks ago, was a shapely round boulder, but which 

 broke to pieces by the pressure necessary to remove it from the earth, and 

 which I now crumble in my fingei's before you. It was a solid stone when it 

 was deposited in the bottom of the Shunganunga; but became decomposed 

 by the small amount of alkali or other deleterious material in the surround- 

 ing soil. Many a story of time, temperatui'e, travels, and attending conditions 

 is written in the bottom of that old Shunganunga, yet to be read by the in- 

 telligent glacial geologist. 



How can we know where these stones were picked up by ice during the 

 Kansan epoch from the place where they were deposited during the last pre- 

 —15 



