TRANSACTIONS OF SECTION B. 827 



recent cold age, which p:eo]ogists call the Pleistocene period. It is impossible for 

 the traveller to overlook the evidences of this so-called Glacial period in the Polar 

 Basin, and whether we seek an explanation of the geographical phenomena from 

 the astronomer or the geologist, or both, it is impossible to ignore the geographical 

 interest of the subject. 



No sciences can be more intimately connected than geography and 



GEOLOGY. 



A knowledge of geography is absolutely essential to the geologist. To dis- 

 criminate between one kind of rock and another is a comparatively small part of 

 the work of the geologist. To ascertain the geographical distribution of the 

 various rocks is a study of profound interest. If the geologist owes much to the 

 geographer, the latter is also largely indebted to the labours of the former. The 

 geology of a mountain range or an extended plain is as important to the physical 

 geographer as the knowledge of anatomy is to the figure painter. 



The geology of the Polar Basin is not very accurately known, and the subject 

 is one too vast to be more than mentioned on an occasion like the present ; "but 

 the evidences of a comparatively recent ice age in eastern America and western 

 Europe are too important to be passed by without a vrord. 



In the sub- Arctic regions of the world there is much evidence to show that the 

 climate has in comparatively recent times been Arctic. The present glaciers of 

 Central Europe were once much greater than they are now, and even in the 

 British Islands glaciers existed during what has been called the ice age, and the 

 evidence of their existence in the form of rocks, upon which they have left their 

 scratches and heaps of stones, which they have deposited in their retreat, 

 are so obvious that he who runs may read. Similar evidence of an ice age is 

 found in North America, and to a limited extent in the Himalayas, but in the 

 alluvial plains of Siberia and North Alaska, as might be expected, no trace of an 

 ice age can be found. 



Croll's hypothesis that an ice age is produced when the eccentricity of the 

 earth's orbit is unusually great has been generally accepted as the most plausible 

 explanation of the facts. It is assumed that during the months of perihelion 

 evaporation is extreme, and that during the months of aphelion the snowfall is 

 considerably increased. The effect of the last period of high eccentricity is supposed 

 to have been much increased by geographical changes. The elevation of the shallow 

 sea which connects Iceland with Greenland on the one hand, and the south of 

 Norway and the British Islands on the other, would greatly increase the accumu- 

 lation of snow and ice in those parts of the Polar Basin where evidence of a 

 recent ice age is now to be found ; whilst the depression of the lowlands on either 

 side of the Ural Mountains, so as to admit the waters of the Mediterranean through 

 the Black and Caspian Seas, might prevent any glaciation in those parts of tlie 

 Polar Basin where no evidence of such a condition is now discoverable. But this 

 is a question that must be left to the geologist to decide. 



The extreme views of the early advocates of the theory of an ice age have 

 been to a large extent abandoned. No one now believes in the former existence of 

 a Polar ice cap, and possibly when the irresistible force of ice-dammed rivers has 

 been fully realised, the estimated area of glaciation may be considerably reduced. 

 The so-called great ice age may have been a great snow age, with local centres of 

 glaciation on the higher grounds. 



The zoological evidence as to the nature, extent, and duration of the ice age 

 has never been carefully collected. The attention of zoologists has unfortunately 

 been too exclusively devoted to the almost hopeless task of theorising upon the 

 causes of evolution, instead of patiently cataloguing its effects. 



There is a mass of evidence bearing directly upon the recent changes in the 

 climate of the Polar Basin to be found in the study of the present geographical 

 distribution of birds. The absence of certain common British forest birds (some of 

 them of circumpolar range sub-generically, if not specifically) from Ireland and the 

 North of Scotland is strong confirmation of the theory that the latter countries 

 were not very long ago outside the limit of forest growth. 



