CENTURY OF IOWA GEOLOGY 423 



a lifetime's devotion of his geological energies to investigation in 

 totatally different fields, should suddenly turn to glacial geology 

 with such signal success, and such notably productive results. In 

 his presidential address before the Geological Society of America, 

 at Baltimore, Professor Calvin gives a summary of the "Present 

 Phase of the Pleistocene Problems in Iowa,"'** in which the five sub- 

 divisions of the Glacial Period are distinctly outlined. These fur- 

 nish the clue to the glacial history of our entire continent and of 

 the world. Comparing these results with what was known twenty 

 years before, it is forecast that another twenty years of effort will 

 disclose other ice advancements of which we now know nothing. 



CLIMATIC INDEX OF INTER-TILL DEPOSITS 



Notwithstanding the fact that continental glaciation is a topic 

 of absorbing interest, it is one of the grand triumphs of modern 

 science to furnish such indisputable proofs that there existed in late 

 geological times a prodigious polar ice-cap reaching so far down as 

 the Ohio and Missouri rivers. Even until a generation or two ago 

 few persons had intimation that an arctic climate had prevailed so 

 recently over so large a part of the northern hemisphere. The con- 

 ception of this veritable Ice Age stands out as one of the scientific 

 novelties of which, says a recent writer, "our century may boast 

 and which no previous century ever so much as faintly adumbrated." 



While the majority of the glacialists were studying the evidences 

 of glaciation one of our own lowan sons. Prof. Frank Leverett, was 

 directing much of his attention to the consideration and analysis 

 of the deposits separating the several till-sheets.-^ So important 

 were his conclusions that we now seem justified in assuming that 

 the warm periods between the successive ice advances were as pro- 

 nounced in their duration as the respective epochs of arctic climate. 

 The necessary inference is that today we are living in the very midst 

 of a typical interglacial time. 



The evidences of these warm interglacial climates are now as 

 abundant and as complete as are those of refrigeration. In supply- 

 ing facts bearing upon this vague phase of the subject Iowa takes 

 first rank. 



SYSTEMATIC REVISION OF THE FOSSIL CRINOIDS 



Since the lamented demise of Doctor Wachsmuth the latter's 

 co-worker, Mr. Frank Springer, has carried on the investigations 



=">Bun. Geol. Soc. America, Vol. XX. pp. 133-152, New York, 190Q 

 =iMon. U. S. Geol. Surv., Vol. XXXVIII, 817 pp., Washington, 1899. 



