RECORDS OF MEETINGS 433 



and history of the loess add a complication to the problem. The best 

 evidence that I saw that the lowan was really a distinct ice-advance, and 

 later than the Kansan, was in a cut of the interurban line that rims from 

 Iowa City to Cedar Rapids. Here the Kansan lies below, bine and clayey 

 and slightly weathered on top. Above this lies the Buchanan (= Sanga- 

 mon) interglacial gravel. This is highly oxidized and ranges in texture 

 from fine flour up to pebbles six or eight inches in diameter. It is roughly 

 stratified, is partly cemented by iron oxides and is brown and l)]ack in 

 color. This gravel and the surface of the Kansan below is thrown into 

 a series of folds, the stratification lines following the folds. These con- 

 tortions can only be explained by a thrust of some kind, and as folding in 

 the deep-seated sense is out of the question, they must be due to pressure 

 from ice. The Kansan also suggests having been overridden by ice, in 

 that it has a series of prominent joint cracks dipping toward the west 

 and suggesting pressure from that direction. On top of the folded beds 

 lie undisturbed drift, of the yellow color characteristic of the lowaii. It 

 is about two feet thick across the top of the folds, but toward the western 

 end of the section the upper till and the Buchanan gi'avel together dip 

 toward the west, the till thickening to about seven feet. Westward it 

 grades into fossiliferous loess, the boundary between loess and lowan drift 

 being almost impossible to draw. There seems no doubt, then, that there 

 was a glaciation in Iowa later than the Kansan; the highly weathered 

 character of the Buchanan points to a long period of deglaciation and 

 hence to a complete retreat of the ice at that time. The question of 

 whether the lowan may be contemporaneous with the Illinoian is more 

 difiicult to prove. Since the lowan ice came from the Kewatin center 

 and the Illinoian from the Laurentide, any comparison of material would 

 be futile. And as Leverett has pointed out, a comparison of the stage of 

 erosion of two places has little significance unless they are nearer than 

 the localities in question. So this phase of the question is still unsettled. 



Mr. Semmes said in abstract: During the summer of 1915 the N'ew 

 York Academy of Sciences, in connection with the Insular Government 

 of Porto Rico, undertook a careful geological survey of a section of the 

 island extending north-south from longitude 66° 06' to 66° 27', or ap- 

 proximately from the city of San Juan to a point about twenty miles to 

 the west. The writer was assigned the northern half of this section, an 

 area extending as far south as the town of Barranquitas. 



On arriving in the field, a topographic map on the scale of two inclies 

 to the mile and 250' contour interval was first made, as a basis for geo- 

 logical observations. 



