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is certain that both agencies were largely employed in sculpturing the 

 rock surface and fashioning the features of our landscape as we now 

 see thein. 



In addition to the more active agents of disturbance just described, 

 others wliich perform their work quite as effectually piobably exist. 

 These are the atmosphere, rains, frosts, winds and the wash and wear of 

 tides and seas. The degrading action of rivers in motion, by which im- 

 mens(3 quantities of matei'ial are removed and carried down and de 

 posited at their mouths, as in the case of the Mississippi, the Nile, and 

 nearer home, the St. Lawrence^ is well known, and from these sources 

 an estimate has been made of the rate of degradation of our continents 

 and the number of yeai-s which would elapse before these would be re- 

 duced to the pre.sent sea level should no further period of upheaval 

 occur. Some idea of the immense force of excavation exercised by 

 running waters can be formed by considering the gi-eat canons of the 

 Colorado, where huge chasms thousands of feet deep have been cut out 

 by the action of streams, sometimes comparatively small, till now these 

 ] (resent some of the most remarkable geological phenomena in the 

 Avoild. It is probable also that the great rock cliffs about this city owe 

 their origin to a gi'eat extent to the wearing action of the rivo-s in this 

 Aicinity. 



With the modified conditions of climate which succeeded the 

 glacial pei'iod, the conditions of life as we now find it began or were re- 

 sumed. Evidences of the presence of tlie human race are visible at 

 the close of tliat jjcriod and even in the interglacial time, wliile some 

 observers contend that human remains have been obtained as far back 

 as the Miocene Tertiary. But with this phase of the subject we have 

 not time sufficient to deal. Gradually the slowly moving fingers of 

 time have fashioned and rounded our hill tops, have carved out the 

 water courses and hewn the basins of our lakes. The action of sun, 

 frost and rain have softened the hard sterile rock and produced the 

 soil necessary for the cultivation of those things required for man's 

 existence. Many if not all of the geological agencies which have been 

 so potent in ))ast ages are in active o[)eration today, though possibly 

 their action is not so marked as under the peculiar conditions of earlier 

 geological times, but they are going forward all tie same. The gradual ^'' 



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