ILLINOIS HORTICULTURAL SOCIETY. 281 



nent is conceded to be larger than Australia, and doubtless all covered 

 with several thousand feet of ice ; then the present continents all 

 widen out and extend high into nortliern latitudes and form regions of 

 ice. If, as in former ages, open seas occupied the place of these polar 

 lands, ice and snow would scarcely be known in this latitude. This 

 great excess of polar lands, is an abnormal condition that did not exist 

 in former ages. 



Formerly, geologists did not hesitate to point out the epoch of 

 time in which life appeared on the globe. But more extended researches 

 have traced organic life through the oldest geological formations known 

 to man ; hence, while it will not be doubted that there was a time be- 

 fore organic forms began to exist, this opinion has not the support of 

 any direct geological evidence. 



The oldest geological section known to man, is the Lawrentian sys- 

 tem of British America formerly considered wholly destitute of any 

 traces of life, and wrongly called Azoic ; but recent discoveries reveal 

 traces of low orders of animal and vegetable life, in the very lowest of 

 the Canada section of rocks accessible to man. 



The total thickness of the Lawrentian system is estimated at about 

 eight miles — all, in the lapse of past eternity, formed in the bottoms of 

 former seas, from sediment worn from still older rocks — perhajjs from 

 the wash and wear of still older continents, of which no vestige is 

 accessible to man ! We must bear in mind that previous formations, 

 are, in all cases, ground up in the mill of time to make each succeed- 

 ing formation. Hence we must see that comparatively little can be 

 left of the older formations. The earth's crust has been so often flexed, 

 broken, and tilted through the succession of ages, that the oldest forma- 

 tions have been mostly ground up by abrasion. 



When we reflect that since the Lawrentian age the total thickness 

 of the stratified rocks of subsequent ages are estimated at over ten 

 miles, we may wonder that this tract of country north of the Great 

 Lakes lies up to the sunlight of the present time as a memorial of ages 

 too remote for human comprehension. 



Such is the nature of geological revolutions — unnoticable to us, 

 only because too slow and gradual for our transient observation. We 

 extend railroads over regions that will be covered with glaciers — build 

 cities on lands that are subsiding into the ocean, and even over the fires 

 of slumbering volcanoes! While at no distant future, wealth will 

 abound on the flood grounds of the Amazon and Mississippi, and orange 

 groves will bloom in the regions of our dismal swamps. Geological 

 revolutions are in progress before our eyes through the same agencies as 

 in all past time. 



As in the physical revolutions of the past ages, so also with the 

 revolutions of the organic world. It has become the incpiiry of the age, 

 whether the solution of this abstruse cpiestion is not to be found in 

 knmvn, fiatural causes, instead of supposing such as are unknown and 

 unnatural. 



