I874-75-] IQI 



gists "Boulder Clay," or "Drift." This singular deposit has only 

 been accounted for at a comparatively recent period. The earlier 

 geologists called it Diluvium, because they supposed it to have been 

 formed by the Deluge. But when it was ascertained that this de- 

 posit is not met with in that region from which the account of the 

 flood has been derived, the idea of its diluvial origin was abandoned. 

 The boulder clay is now believed to have been formed by a capping 

 of glacial ice, which at some remote period covered the greater part 

 of the land in northern and southern latitudes. A similar ice cap 

 covers the northern part of Greenland at present as well as those 

 almost unknown lands in the Southern Ocean. 



Various causes have been assigned for the vast difference in 

 climate necessary to produce such phenomena. Some hold that 

 it may have been brought about by a different degree of inclination 

 of the earth's axis to the plane of its orbit, combined with a greater 

 amount of eccentricity in the orbit itself. Others consider that it 

 may have, been caused by a different distribution of land and water, 

 accompanied by a different direction of cold and warm oceanic cur- 

 rents. Whatever may be the cause or causes, there is unmistaka- 

 ble evidence that the climate of any particular district of the earth's 

 surface is not at all permanent. The representatives of plants and 

 animals now inhabiting tropical regions once lived in England, and 

 remains of the reindeer, an animal confined at present to the ex- 

 treme north, have been found as far south as the Pyrenees. On 

 the other hand, the remains of large forest trees recently discovered 

 in Greenland, show that that inhospitable region has not always 

 been doomed to perpetual ice. 



There is evidence that several glacial periods have taken place 

 in remote ages, separated by long intervals, in which a milder cli- 

 mate prevailed. It is, however, with the last of these episodes 

 that I am to deal at present. The date of this event has not been 

 determined with any approach to accuracy ; but, compared to the 

 time that has taken place since the formation of our coal-fields, or 

 even since the deposition of the white limestone of our coasts, it 

 is but as yesterday. Hence the rock matter formed in tlus way 



