Transactions. 85 



II. Theories of the Ice Age and Notes on the Glacial Geology of the 



immediate Neighbourhood. By Mr James Watt. 



(Epitomised by the author.) 



The primary cause of great variations of climate is the 

 position of the earth in relation to the Sun. 



Glacial conditions ensued in consecjuence of {a) a gradual 

 increase of ellipticity of the earth's orbit until it reached a period 

 of maximum eccentricity, or extreme elliptical form ; (/') the 

 precession of the equinoxes. 



The combined effect of these two causes must, to a very large 

 extent, influence the climate of the earth, because from precessional 

 movement when the winter solstice in the northern hemisphere 

 occurs when the earth is furthest from the sun in June, not as 

 now in December, when it is nearest, and also, when from greater 

 ellipticity of the orbit, the distance of the earth from the run is, 

 in the Avinter solstice, several millions of miles greater than now, 

 then, in such circumstances, glacial conditions of excessive severity 

 would prevail. 



Sir Charles LyaU, in his great work on the " Principles of 

 Geology," showed conclusively that changes in the geography of 

 the globe, combined with precession, would aecount for great 

 changes of climate. But it was not till the appearance in 1864 of 

 Dr James Croll's remarkable paper, "On the ph^-sical cause of 

 change of climate during Geological Epochs," that it became clear 

 that the primary cause of g.reat variations of climate was astro- 

 nomical. Dr CroU made calculations for the form of the earth's 

 orbit from the year 1800 for three millions of years back, and one 

 million of years forward, calculated at intervals of 50,000 years, 

 and his calculations have been verified by eminent mathematicians 

 in Europe and America. According to these calculations, the 

 period of the last great increase in the ellipticity of the earth's 

 orbit was reached 240,000 years back, and terminated about 

 80,000 years ago, embracing a period of 160,000 years. That 

 period we call the " Great Ice Age," or " Glacial Epoch." The 

 cold was most intense about 200,000 or 210,000 years ago, and it 

 is maintained by Croll and other eminent men that glacial condi- 

 tions during the period of high eccentricity would not be continu- 

 ous in northern and southern hemispheres, but that each hemisphere 

 " must have," in Professor James Geikie's own words, " experi- 

 enced several great vicissitudes of climate. Glacial conditions 



