544 THE GEOLOGY OF MINNESOTA. 



[Terminal moraine. Loess 



Terminal moraine. The outer'terminal moraine, formed at the border 

 of the ice-sheet of the last glacial epoch, when it reached its maximum ex- 

 tent, lies in the northeast part of Pipestone county, which it enters from 

 the southeast in sections 12 and 13, Rock, thence running northwest and 

 passing into Lincoln county at the north side of sections 1 and 2, Fountain 

 Prairie. The moraine here varies from one to two miles in width, and 

 forms the crest of the broad area of highland called the Coteau des Prairies. 

 In northeastern Rock, and from section 35 to section 28, JEtna, it consists 

 of very roughly and prominently hilly till, diversified by many knolls and 

 short ridges, of no well-marked uniformity in trend, much in contrast with 

 the smooth surface of till, in long, gentle slopes and swells, lying 100 to 150 

 feet below this moraine upon each side. The till or boulder-clay constitut- 

 ing the moraine seems to differ from the same deposit in the smooth tracts 

 only in containing a very much larger proportion of boulders and pebbles, 

 which on the morainic hills and ridges are commonly at least twenty times 

 and often evidently more than a hundred times as plentiful as they aver- 

 age upon the ordinary moderately undulating areas of till. Many of the 

 knolls and hillocks of this moraine in ^Etna are very stony with rock-frag- 

 ments of all sizes up to five or six feet in diameter, mostly, however, not 

 exceeding half this size. The water-courses on the flanks of this massive, 

 knolly ridge are deep, steep-sided ravines; and sloughs and lakelets are 

 rare. From the south part of section 20, J^ina, the next three miles of 

 this moraine northwesterly are less knolly than usual; but farther to the 

 northwest it is as irregularly broken as in southern ^Etna and northeast- 

 ern Rock. UPHAM. 



Loam-clay. The plate (No. 23) which represents these counties is so 

 colored as to indicate an extension of the loess-loam of the Missouri valley 

 over a small area in the southwestern part of Rock county; but it should 

 also be added that this extension is limited rather by an ideal than an act- 

 ual boundary, and is designed to include only that area which shows an 

 unequivocal aqueous action in the form of more or less stratified clay. A 

 gravelly clay, which, as already stated, seems to graduate on the one hand 

 into the loam, and on the other into the common till, is found on the sur- 

 face some miles farther north, but it is here colored as if a part of the till.* 



The sixth annual report, p. 1W. 



