BEVIEW OF GEOLOGICAL STRUCTURE. 49 



fitted by experience and sagacity for giving a full and accurate reading 

 of the facts before them. Naturally, this testimony is often discordant, 

 and not being able to discriminate between the true and the false, the 

 local and the general, he has been led by it into some errors, which are 

 the more to be regretted since they are endorsed by his high authority, 

 and are published in by far the best history of the Drift period yet writ- 

 ten. For the errors into which he has fallen in regard to the Surface 

 Geology of Ohio, he is mainly indebted to Prof. N. H. Winchell, who has 

 observed the Drift phenomena in the north-western portion of the State 

 only, and there his observations are not fully in accord with those made 

 by others. 



On page 462, Professor Geikie says : " The succession of changes in 

 Ohio during the Drift period were, according to Professor Newberry, as 

 follows : 



First. A period of a great continental glacier or ice sheet. 



Second. The retreat of the ice and the appearance of a vast fresh 

 water lake, covering a large part of Ohio, in which were deposited the 

 finely laminated Erie clays, etc. 



Third. The silting up of the lake, and the advent of a luxuriant forest 

 growth. 



Fourth. The submergence of the land below a great inland sea of 

 fresh water, and the deposition from floating ice of blocks and bowlders. 



Those who have read the transcript of Drift history, given in our 

 Chapter XXX, will see that this is not accuratelj^ epitomised in the par- 

 agraphs above quoted ; inasmuch as it has been nowhere stated by the 

 writer that the lake basin was ever silted up so as to bpcome a land sur- 

 face, covered with forest, nor that there was any second submergence of 

 the lake basin. The true order of succession of events in the history of 

 the lake basin, as believed and represented by the writer is, very briefly, 

 as follows : 



First. A pre-glacial continent, several hundred feet higher than now, 

 deeply scored by drainage lines, now the buried river channels. 



Second. The advent of the ice period, producing, first, local, then 

 general, and, again, local glaciers, which ground down, scratched, and 

 grooved the surface rocks, filling and obliterating many of the old chan- 

 nels, and scooping out the lake basins. 



Third. The retreat of the glaciers, leaving the Bowlder clay as a wide- 

 sj)read sheet of unwashed morainic material, covering the glaciated sur 

 face ; over this a body of fresh water, which formed a great inland sea, on 

 which ice rafts floated from the north southerly, scattering bowlders 

 broadcast over the bottom. 

 4 



