TWENTY-SEVENTH ANNUAL MEETING. 223 



the question as to whether they were transported by glaciers coming from 

 the north has received serious consideration. The iceberg question must 

 be decided in the negative, because icebe^jgs scatter and deposit their loads 

 everywhere over their courses in warmer seas. These stones, on the con- 

 trary, are scattered in a very definite line, a line which is continuous in all 

 its course of more than 2,000 miles, except where it can be shown to be broken 

 through local causes. 



CAUSES OF THE ICE PERIOD. 



Whether these stones have been carried by ice from the north, over dry 

 land, raises the question as to what the climate must have been in past ages 

 to cause such a degi-ee of cold as to allow glaciers to accumulate to an extent 

 sufficient to reach as far southward as Kansas and southern Illinois. 



The question of change of position of the poles and consequent change of 

 all latitudes on the earth is too absurd to merit serious consideration. That 

 there is a very small change going on I will not deny. But the oblateness and 

 fixity of the earth will preclude the possibility of a change of latitude at any 

 place sufficient to affect the climate. 



The question of land elevation as a cause of the glacial epoch has received 

 serious consideration and some believers. But the arguments are specious; 

 they are based on false premises. Elevation and depression of the northei'n 

 hemisphere is a regular result of the earth's astronomical changes, not a cause. 

 If elevation were a cause, the greatest extent of ice should be looked for in the 

 highest regions. But the greatest extent of ice occurred in the low lands of 

 Illinois and Indiana, while the elevated regions of the northern peninsula 

 of Michigan and of Cattaraugus county, New York, proved an effectual barrier 

 to the passage of the ice over them; and the elevated region of the "great 

 plains" had free running streams every summer, while Iowa, north Missouri, 

 and all the low plain region east to western Pennsylvania Avas covered with ice 

 for a thousand years. 



If glaciation of the northern hemisphere is not brought about by terres- 

 trial causes, it is well to consider the astronomical changes that could tend 

 to bring about such a result: 



First. Ellipticity of the earth's orbit and precession of the equinoxes. 

 If the earth's orbit were a true circle, the summer and winter would be equal 

 in length. As it is, the six months of summer is now six days longer than 

 the six months of winter. The perihelion point of the earth is reached about 

 the first of January. This point recedes in the orbit a little, so that the 

 earth reaches it 50 seconds of space earlier each year, and makes the com- 

 plete I'ound of the earth's orbit in 25,868 years. This is called a platonic 

 year. Progression of the perihelion point of the earth's orbit (11 seconds per 

 year) is added to this, making 61 seconds of space each year and reducing the 

 platonic year to 21,408 years. 



The heat at present received in the northern hemisphere in summer, com- 

 pared with that received in winter is as 176 to 100. In 13,000 years more, when 

 the earth reaches its perihelion on the 4th of July, and the platonic winter 

 comes to the northern hemisphere, the amount of heat received in the sum- 

 mer season as compared with that received during the winter season will 

 be as 160 to 100. Thus, comparing 176 with 160 the northern hemisphere 

 receives 10 per cent, less heat each summer during the platonic winter than 

 during the present summers. This 10 per cent, distributed over the northern 

 hemisphere would vary fi'om nothing at the equator to 10 per cent, in the 

 latitude of Kansas and 23 per cent, around the north pole. Ten per cent, of re- 



