10 PROCEEDINGS OF THE BOSTON MEETING 



of the ice, causing it to retreat, and probably giving to it a mainly steeper frontal 

 gradient than during its growth and culmination. To this steeper gradient and 

 consequently more vigorous glacial currents I attribute the larger morainic accumu- 

 lations of drift marking retreatal stages, both in North America and Europe, than 

 on the outermost drift boundaries. 



When the ice had considerably receded the outer portions of the depressed areas 

 were somewhat uplifted to approximately their present height, which they have 

 since held, excepting minor oscillations. Gradually as the ice-sheet of our conti- 

 nent withdrew from south to north a principally permanent wave of land eleva- 

 tion has followed, earliest uplifting the loess region of the Mississippi basin, later 

 the areas of lake Agassiz, of the Laurentian lakes, including lake Champlain, and 

 of the Saint Lawrence valley, and latest the country surrounding Hudson bay, 

 where this movement is still in progress. The time since the departure of the ice 

 there has been too short, as in Scandinavia, to allow the earth's crust yet to have 

 completed its restoration to an isotatic condition. 



Remarks upon Mr Upham's paper were made by Professor D. S. 

 Martin and J. W. Spencer. 



The next paper was entitled : 



CLAYEY BANDS OF THE GLACIAL CUYAHOGA DELTA AT CLEVELAND, OHIO, COM- 

 PARED WITH THOSE AT TRENTON, NEW JERSEY 



BY C. FREDERICK WRIGHT 



The next two papers were read by title. 



MIDDLE COAL MEASURES OF THE WESTERN INTERIOR COAL FIELDS 

 BY H. FOSTER BAIN AND A. G. LEONARD 



lAbstracf] 



The moat important coalfield west of the Mississippi, so far as present develop- 

 ment is concerned, is that which stretches from north-central Iowa across portions 

 of Missouri, Nebraska, Kansas, Arkansas, Indian Territory, and into Texas. In 

 recent years there has been a good deal of geological work done within this field, 

 and some of the older conceptions of its stratigraphy are being changed. It is 

 proposed to discuss here certain problems relating especially to the northern end 

 of the field, that portion extending from central Iowa to southwestern Kansas. 



The change from the condition obtaining in the early Des Moines to those pres- 

 ent when the Missouiian began was a gradual one. During the former period 

 there was no uniformity anywhere and the field was broken up into a multitude 

 of minor basins of deposition, each the theater of an individual sequence of events, 

 while during the latter the whole of southwestern Iowa, northwestern Missouri, 

 eastern Kansas, and probably an even larger area acted as a unit. The turbulent 

 conditions of the earlier period became merged into the uniform conditions of the 

 later one. Gradually larger and larger areas came to act together and local 

 sequences became of wider and wider applicability. It is the beds of this inter- 



