ILLINOIS HORTICULTURAL SOCIETY. 279 



geological period comparatively recent, it was a land of broad lakes and 

 numerous rivers. Huge beasts moved through the forests with heavy 

 tread, the hippopotamus wallowed in the mud of the lakes, herds of 

 wild horses, cattle, camels, antelopes and deer, fed on grassy plains, 

 carnivorous beasts met in deadly conflict, or lay in wait to seize the 

 the herbivorous animals as they came to the streams to quench their 

 thirst. The bones of these animals were washed down into the lakes 

 by the next flooding of the streams, where they were buried in the mud 

 and preserved for our inspection. The beds of former rivers, that were 

 once overhung by sylvan scenery, and abounded with fish, are now ob- 

 scurely traced in arid sands. Sage brush abounds where once rolled 

 the waves of extended lakes. The petrified form of a huge turtle occa- 

 sionally appears to tell the tale of former times. No falling rains now 

 saturate the earth to carry away the alkali that has accumulated from 

 the decomposition of feldspathic rocks. 



Such are among the physical changes that relate to geological epochs 

 comparatively recent. And let us bear in mind that these changes, of 

 which geologists have become cognizant, are probably but a minor part 

 of what have actually occurred. If nearly half of our present continents 

 have been redeemed from the ocean since, or during the miocene peri- 

 od, it must be considered more than probable that a corresponding 

 portion of older lands have subsided beneath the oceans in the same 

 time. And, we may add, more than probable that regions where the 

 mastodon and elephant once roved through majestic forests, aye, regions 

 that gave origin to many of the higher forms of life, may now lie beneath 

 the waves of our present oceans. 



Many people fall into the error of supposing that our geological 

 maps show the actual outline of the continents for the different geolog- 

 ical periods. Geological maps are intended to show only the fractional 

 portion that is now above water that relate to the different periods. 

 Large areas relate to the sand periods of which we have no knowl- 

 edge ; because submerged by our present oceans. It cannot be sup- 

 posed that our present continents exhibit more than a fractional portion 

 of what was the dry lands of the older ages. Lyell assures us that the 

 portions of the earth's surface overspread by our present oceans, if ac- 

 cessible to man, would reveal vastly more of the geological history than 

 the portion that is above water. 



Persons who have had little time or opportunity for geological 

 study often get the impression that the geological record presents well- 

 defmed lines, showing the beginning and ending of each geological 

 period; also the exact line where organic life first began to exist ; and 

 the exact lines where the different orders of life began to exist. These 

 are mistakes. No such lines are distinctly defined. It is true that 

 distinct lines frequently occur in the rocks, caused by local physical 

 changes. Such lines occur where a portion of the geological record is 

 wanting, and have only a local extent. Geological ages are only arbi- 

 trary divisions of geological time. We have no reason to suppose any 



