422 IOWA ACADEMY OF SCIENCE Vol. XXVI, 1919 



cupied, but, as well, the canons by which it was cleft, the floe-bear- 

 ing lakes and mud-charged marshes with which it was fringed, each 

 island of ice, and each ice-bound lake formed within its limits. And 

 it is not only necessary to reconstruct the geography of a dozen 

 episodes, as does the anatomist the skeleton from a few bones, but 

 to develop the geography such as civilized eye has never seen, and 

 which could exist under conditions such as utterly transcend the 

 experience of civilized man. All this has been done. The trail of 

 the ice monster has been traced, his magnitude measured, his form 

 and even his features figured forth, and all from the slime of his 

 body alone, where even his characteristic tracks fail." 



COMPLEXITY OF THE GREAT ICE AGE 



Iowa's role in the establishment of glacial succession was pecu- 

 liarly fortunate. In the world-wide controversy which raged for 

 more than a generation our state bore a conspicuous part. It was 

 in Iowa that the first real evidences were found indicating a multi- 

 ple instead of a unal character for the Glacial Period. They were 

 Iowa men who made this telling discovery. In Iowa were difl^er- 

 entiated not one but five prodigious drift sheets marking successive 

 advancements of the vast fields of northern ice. On Iowa men de- 

 volved mainly the responsibility of first working out the complete 

 and genetic relationships of these remarkable till mantles. Today 

 the Iowa classification of the great Ice Age epochs is accepted by 

 the whole world. 



In order fully to appreciate the genuine importance of the Iowa 

 results bearing upon glacial complexity as opposed to glacial unity 

 the facts leading up to the birth of the conception may be briefly 

 reviewed. So early as 1870 Edward Orton observed peatbeds inter- 

 calated in the glacial deposits of Ohio, and he rightly concluded, as 

 it afterwards proved, that this feature indicated a warm interglacial 

 epoch. He stated that evidences were now at hand for an orderly 

 arrangement of post-Tertiary deposits. This dual aspect of the 

 glacial debris was further substantiated by Leverett, Chamberlin, 

 Gilbert, McGee and others. In the prolix discussion which neces- 

 sarily followed, on the duality of the Glacial Period, the real facts 

 were overlooked or misinterpreted, and the possibility of a multiple 

 instead of either a unal or dual Ice Age was lost sight of completely. 

 Once suggested, however, the multiple hypothesis, about the year 

 1893, gained general acceptance among scientific men. 



It is a quite noteworthy circumstance, as Prof. R. D. Salisbury 

 recently points out, that Prof. Samuel Calvin, of Iowa, who. after 



