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crust, as regards elevation and submergence, througliout eacla one of the 

 great systems into which the geological scale has been divided. 



We have now reached in our hasty sketch that portion of the 

 earth's history which is most closely related to our own time, viz., the 

 Post-tertiary, the phenomena of which are generally discussed under 

 the head of superficial geology. At the close of the Pliocene or last 

 of the divisions of the Cenozoic or Tertiary a great change of conditions 

 as regards the sui'face of much of the globe evidently took place, intro- 

 ducing what is known as the glacial epoch, a time of intense cold, 

 when large areas of the northern hemisphere, at least, Ijecame covered 

 with ice, which extended probably over the whole or greater part of 

 Canada. Whether similar glacial conditions occurred at earlier stages 

 of the earth's history is a subject which has evoked considerable discus- 

 sion, some eminent authorities maintaining that the evidence of such 

 ice action, as seen in the presence of glaciated or striated stones in 

 conglomerates, are clearly visible even as far back as the Paleozoic 

 time. It would be out of place here, even did time permit, to discuss 

 the causes that led to the changes in the climate of this period, such 

 considerations more properly belonging to the domain of the astronomer 

 and physicist. 



The last of the geological periods, that now under consideration, 

 is also styled the Quaternary or Post-pliocone. It is generally divided 

 into two parts, the first known as pleistocene or diluvial, in which 

 many of the mammals are of species now extinct, and the alluvial or 

 recent, in which all or nearly all the mammals are of still living species. 

 The indications of a change of climate at the close of the Tertiary are 

 seen in the character of the organic life of that time, and it affected the 

 higher latitudes both of the old and new worlds. The cold gradually 

 increased until the conditions now prevailing in Greenland reached a 

 latitude of about 39^ in Eastern America. Over a great part of the 

 hemisphere north ot this parallel it is held by many that a great ice 

 cap, many hundreds and even thousands of feet in thickness, covered 

 the surface, which, following the law of glaciers, moved steadily but 

 slowly forward. The effect of the movement of so vast a body of ice 

 was of necessity to remove the soil and superficial deposits and to 



