616 KANSAS CITY REVIEW OF SCIENCE. 



Let us go back, in time, to the genesis of our Continent. There was once 

 a time in the history of the Earth, when all the rocks were in a molten condition, 

 and the waters of our great oceans in a state of vapor, surrounding the fiery ball. 

 Space is intensely cold. In course of time the Earth cooled off, and on the cold, 

 solid crust geological agencies began to work. It is now conceded by the most 

 accomplished physicists, that the location of the great continents and seas was 

 determined by the original contraction and cooling of the Earth's crust; though 

 very greatly modified by a long succession of changes, produced by the agencies 

 of "water, air, heat, and cold," through probably a hundred millions of years, 

 until the original rock surface of the Earth has been worked over to a depth of 

 thirty or forty miles. 



Like human histories, the events of these long csons are divided into periods. 

 The geologist divides the past history of the Earth and its inhabitants into five 

 Great Times ; and these again, into ages, periods, epochs and eras. 



At the close of the first Great Time — called Archaean — the Continent south of 

 the region of the great lakes, excepting a few islands, was still submerged be- 

 neath a shallow sea, and therefore no portion of the Mississippi was yet in ex- 

 istence. At the close of the second great geological Time — the Palaeozoic — the 

 American Continent had emerged sufficiently from the ocean bed to permit the 

 flow of the Ohio, and of the Mississippi, above the mouth of the former river, 

 although they were not yet united. 



Throughout the third great geological Time — the Mesozoic — these rivers 

 grew in importance, and the lowest portions of the Missouri began to form a trib- 

 utary of some size. Still the Ohio had not united with the Mississippi, and both 

 of these rivers emptied into an arm of the Mexican Gulf, which then reached to 

 a short distance above what is now their junction. 



In point of time, the Ohio is probably older than the Mississippi, but the 

 latter river grew and eventually absorbed the Ohio as a tributary. 



In the early part of the fourth great geological Time — the Coenozoic — near- 

 ly the whole continent was above water. Still the Gulf of Mexico covered a 

 considerable portion of the extreme southern States, and one of its bays, extend- 

 ed as far north as the mouth of the Ohio, which had not yet become a tributary 

 of the Mississippi. The Missouri throughout its entire length was at this time a 

 flowing river. 



I told you that the Earth's crust had been worked over to a depth of many 

 miles since geological time first commenced. Subsequently, I have referred to 

 the growth of the Continent in different geological periods. All of our continents 

 are being gradually worn down by the action of rains, rills, rivulets and rivers, 

 and being deposited along the sea margins, just as the Mississippi is gradually 

 stretching out into the Gulf, by the deposition of the muds of the delta. This 

 encroachment on the Gulf of Mexico may continue, yea, doubtless will, until that 

 deep body of water shall have been filled up by the remains of the Continent, 

 borne down by the rivers ; for the Mississippi alone carries annually 268 cubic 

 miles of mud into the Gulf, according to Humphreys and Abbot. This repre- 



