the Middle Atlantic Slope. 



459 



Kansas, Missouri, southern Iowa, Illinois, Indiana and south- 

 western Ohio, and indeed appears to be a continuation of the 

 Port Hudson formation of the lower Mississippi as defined by 

 Hilgard, thus indicating that during the earlier period of cold 

 the central Mississippi valley was submerged — the far greater 

 antiquity of the earlier till and " gumbo " than of their later 

 homologues (the upper till and loess) being indicated by the 

 intervening forest bed, by the greater disintegration and ferru- 

 gination of the older materials and by the far greater degrada- 

 tion beyond the limits of the newer deposits,* while there is 

 much less indication of considerable lapse of time after the 

 deposition of the loess and before the deposition of the super- 

 jacent moraine-fringed drift-sheet. So the Iowa-Missouri 

 sequence in historic order is, (1) first glacial drift (basal till) 

 passing upward into waterlaid clays with erratics ("gumbo"), 

 (2) great unconformity and forest bed, (3) second till passing 

 upward into or overlain by loess, (4) inconspicuous unconfor- 

 mity, and (5) third till apparently connected with the terminal 

 moraine. 



The glacial phenomena of Northern United States have been 

 elaborately investigated by Chamberlin and found to contain a 

 definite record of the events constituting the glacial history of 

 the continent. His allocation of leading episodes in the his- 

 toric order is as follows : 



Epochs. Subepochs or episodes. Attendant or characteristic phenomena. 



I. Transition epoch. Not yet satisfactorily 

 distinguished from 

 the Pliocene, 

 f f Drift sheet with attenuated bor- 



First subepoch or epi-j der; absence or meagerness of 

 sode. j coarse ultra-marginal drainage 



L drift. 

 \ Interglacial subepoch or j Decomposition, oxidation, ferru- 



IL Earlier gla- 

 cial epoch. 



episode of glaciatiou. 



Second subepoch or epi- 

 sode. 



III. Chief interglacial epoch 



IV. Later glacial j 

 epoch. ] 



/ gination ; vegetal accumulation. 

 r Drift sheet with attenuated bor- 

 \ der ; loess contemporaneous 



with closing stage. 

 ' Elevation of the Upper Mississippi 

 region 1,000 ± feet. Erosion of 

 old drift, decomposition, oxida- 

 tion, ferrugination, vegetal accu- 

 (_ mulations 



f First episode or sub- j Till sheet bordered by the Kettle 

 epoch. I or Altamont moraine. 



Episode of deglaciation. Vegetal deposits 



c j . , , LTill sheet bordered by the Gary 



Second stage or subepoch. -f j j 



1 ( moraine. 



Episode of deglaciation. 



Third enisode 1 Til1 bordered b F the Antelope mo- 



1 ( raine. 



Later stages .. \ Marked b 7 . terminal moraines of 



Am. Jour, Sci. 



28 



" I undetermined importance. 

 * Trans. St. Louis Academy of Sciences (in press). 



Third Series, Vol. XXXV, No. 210.— June, II 



