ANOTHER POSSIBLE CAUSE OP THE GLACIAL EPOCH. 149 



months in the year ; lastly, tlie mountains of North Norway 

 and Lapland and the frigid tracts of Siberia bordering the 

 ocean, where the soil is permanently frozen a few inches 

 below the surface ; of all these regions it may be said, that if 

 their temperature ever rises above freezing point of water, it 

 is only to the extent of a very few degrees during the three 

 summer months.* 



Isotherm of 42° Fahr. — Very different is the climate 

 enjoyed b}^ those regions lying under the isothermal line of 

 42°. Leaving the western coast of America at Vancouver 

 it crosses that continent by the Great Lakes to Nova Scotia 

 in lat. 45° N. ; then driven northwards by the Gulf Stream 

 it crosses the (iOth parallel half-way between Iceland and 

 Scotland and reaches the coast of Norway a little north of 

 Bergen, then curving round the southern shores of Scandi- 

 navia, passes into Russia south of St. Petersburg, and crosses 

 Central Asia near the intersection of the parallel of 45° N. 

 by the meridian of 90° E. This isotherm, except when it 

 passes over the Atlantic, is characterized by extremes of 

 heat and cold ; but the heat predominates, and glacial 

 conditions are impossible except at high altitudes such as 

 are afforded by the mountains of Norway. 



Effect of the conversion of the isotlierm of 42" into that of 32°. 

 — We are safe in supposing that if the isotherm of 32° once 

 occupied the position of 42° of the present day, the 

 climate along this line was very different from that which 

 now prevails; let us endeavour to define its conditions in 

 outline. 



As regards America it may be inferred that the Great 

 Lakes were in their northern portions permanently frozen 

 over like the waters of Hudson Bay throughout eight 

 months in the year, while Labrador and the lands lying 

 along the western shore of Hudson Bay and extending to the 

 shores of the Great Lakes were covered by snow which the 

 sun of summer would be unable to melt. There Avould 



* The following are some of the tempeiature observations within the 

 Polar regions : — 



Three Three 



Summer Winter An. mean 



Months. Months. temp. 



Banks' Land Lat. 74° N. + 35° — 5° '7 -f l^'S Fahr. 



Parry Island „ 74° 25' +37° —10-6 + 1°-4 „ 



Cornwallis Island „ 74° 45 +36° —8-6 + 2°-5 „ 

 Northumberland 



Sound „ 77°0 + 30°-8 — ll'S — T'l , 



