ILLINOIS HORTICULTURAL SOCIETY. 27 



For example, it is well known that, at the present time, Greenland is 

 subsiding, while Scandinavia is being elevated. These oscillations are 

 extremely slow — not generally to exceed one or two feet in a century ; 

 but when long continued they must effect momentous revolutions in 

 climatic changes, and also in the configuration of land and water. 



Now these oscillations of the earth's surface, and various other phe- 

 nomena, prove that the outer portion of the earth consists of a flexible 

 crust ; for if it was solid to the center, it could neither bend down, nor 

 rise up; — hut It ^/ocs />e//t/. Such oscillations of the earth's crust are 

 among the known physical changes that are constantly going on at the 

 present time ; and the geological record bears ample evidence that such 

 changes have been going on in all i)ast time. It is now conceded that 

 it is mainly through these slow oscillations of the eartli's crust, accom- 

 panied by the abrading action of water, that the most extensive geolog- 

 ical revolutions of past ages have been effected. The configuration of 

 land and water has been ever changing. Hence the present geography 

 of the earth bears no resemblance to any remote age of the past, and 

 probably no resemblance to any remote age of the future. 



Every portion of dry land bears unmistakable evidence of having 

 been in past ages, for long durations of time, beneath the oceans, and in 

 most cases, of several successive changes, from ocean to land, and from 

 land to ocean again. Probably every portion of the earth's surface that 

 is now covered by oceans has been, in past ages, in the condition of dry 

 land ; and, as we have reason to believe, will, some time in future eter- 

 nity, again form portions of other continents. 



All rocks known to geologists (except the igneous rocks of trap- 

 dykes and volcanic rocks) bear evidence of having been formed of the 

 accumulations in the bottoms of former seas. Accumulations are being 

 formed into rocks in our present oceans as in all past time, and by a 

 like process. The wash and wear of continents are being transported 

 by rivers to the ocean ; this sediment is carried by currents and spread 

 over the floors of the ocean ; and mingled with this sediment are pre- 

 served the forms of life that exist in our great seas. All the ledges of 

 limestones on the earth have originated from material that has passed 

 through the secretions of low orders of marine life. Mollusks and co- 

 rals are at work in our present seas in collecting material for building 

 up ledges of limestones, as in all past time. This is especially a chalk- 

 making period. For sixteen hundred miles of the ocean plateau on 

 which the Atlantic cable is laid, microscopic forms of life are incessantly 

 at work in the manufacture of chalk. These low forms of life are not 

 distinguishable under the microscope from those of the cretaceous 

 chalks of Europe. 



The earth's surface still rocks beneath our feet with earthquake 

 shocks, and volcanoes pour forth volumes of lava. It is true that there 

 is some evidence that volcanic action may have occurred on a larger 

 scale in former ages ; but the geological record gives no evidence of 

 more frequent, or more extensive oscillations of the earth's crust, in 



