308 



LECTURE XL 



The Diluvial Period.— Eevolutions and Transitions.— Glacial formation.— 

 Boulder-Clay.— Old AUuvium.— Terminal Moraines and Erratic Blocks. 

 —Slate-Coal, and its Formation. — Ice-sea and Glacial Foi-mation in the 

 North— In England.— Table of Diluvial Strata.— Length of Time.— 

 Chronological Calculations in the Deltas of the Mississippi and the Nile. 

 — Impossibility of a Universal Deluge. 



GentlemeNj — Our investigations concerning man's aj)pear- 

 ance upon the globe have, indeed, furnished us with a clue as 

 to the geological period in which that event occurred, but 

 leave us in the dark as to the determination of the year or cen- 

 tury. With regard to the geological period, we may state at 

 once that it is the last period we treat of, since which there has 

 apparently been no interruption down to the present time. We 

 possess, at present, no facts for determining the age of human 

 fossils calculated by centuries or millenniums. All that we are 

 entitled to say is, that these remains are very old, reaching far 

 beyond the time assigned by current traditions and legends 

 concerning man and the creation of the earth. When treating 

 of more recent remains we shall have an opportunity of men- 

 tioning the attempts which have been made chronologically to 

 determine the age of some rehcs from the overlying strata in 

 which they were found. For the present, we shall consider 

 the geological period in which man first appeared. 



I must beffin with a confession. There was a time when 

 the history of the earth was construed from individual, inde- 

 pendent periods, separated from each other by mighty revolu- 

 tions. It was assumed that, during the intervening periods of 

 rest, a new creation arose, propagating and accumulating until 

 the crust of the earth suddenly bursting, chains of mountains 

 were formed, vast regions became submerged, and sea- 

 covered tracts laid bare. After every revolution, which des- 



