88 THE GLACIAL LAKE AGASSIZ. 



Mississippi, containing' Margaritana and Unto, with a thin seam of Ugnite 

 and hgnitic clay. All the Cretaceous deposits of western Minnesota, except 

 in the high Coteau des Prairies, now exist only as a somewhat thin and 

 often discontinuous sheet, ranging in thickness up to maxima of probably 

 nowhere more than 100 to 300 or 600 feet, on the Archean, Algonkian, and 

 Silurian rocks. They are doubtless remnants of the base of a considerable 

 thickness of strata, perhaps originally including the entire Cretaceous series 

 of the Northwest, from the Dakota to the Laramie. 



A section of the drift and Cretaceous beds forming the eastern foot- 

 slope of the Coteau des Prairies is reported by Prof. N. H. Winchell from a 

 well at Tracy, about 60 miles west of New Ulm, 619 feet above the Min- 

 nesota River at that place, and 1,403 feet above the sea-level. Till extends 

 from the sm-face to the depth of 120 feet; next is fine gravel, largely of 

 limestone, 5 feet, including also fine sand and soil-like matter, believed by 

 Professor Winchell to be "a remnant of the old soil which accumulated on 

 the Cretaceous rocks during the Tertiary age;" under this is fine blue 

 clay, 20 feet; then a second bed of gravel, 20 feet, containing pebbles of 

 buff limestone and of gray and dark or reddish quartzite, also of gray 

 conglomerate or coarse sandstone, ranging in size from an inch in diameter 

 to sand grains, with much slag and traces of lignite, from which characters, 

 according to Professor Winchell, this bed "can be supposed to have 

 accumulated on the Cretaceous after the withdrawal of the Cretaceous 

 ocean, the slag coining from the combustion of the lignites contained in 

 the strata." From the bottom of this gravel, at the depth of 165 feet, 

 Cretaceous beds of clay, shale, and sandstone reach 525 feet, having a 

 prevailingly dark color for 446 feet, but mostly white for the lower 79 feet. 

 In descending order, they are fine blue clay, 12 feet; fine greenish-blue 

 sandstone, 20 feet; dark-gray shale, 213 feet; again, fine greenish-blue 

 sand, 60 feet; blue clay or shale, 43 feet; quartzitic white sandstone, with 

 concretionary pyrite, 32 feet; fine gray sandstone, 5 feet; again, blue clay 

 or shale, 30 feet; a second layer of quartzitic and pyritous white sandstone, 

 V feet; dark, unctuous, fine clay, 24 feet; white kaolinic clay, becoming- 

 reddish, then bluish and gritty, 8 feet; white and gra}' quartz sand, partly 

 cemented by pyrite and nnxed in its lower part with kaolinic clay, 18 feet; 



