THE PRE-WISCONSIN DRIFT OF NORTH DAKOTA 



527 



bed is composed of bowlders of all sizes, those from 2 to 3 feet in 

 diameter being quite common, though those less than 1 foot in 

 diameter are most abundant. One sandstone bowlder measured 

 14 feet in length, another was 9 feet long, and another 4 feet. 

 Granite, limestone, petrified wood, and sandstone bowlders are 

 found, together with other kinds of rock. The interstices between 

 the coarser materials are filled with gravel and sand, and the whole 

 deposit is cemented into a rather firm, indurated mass. It is 

 very ferruginous and brown from the limonite forming the cement- 

 ing material, and in many places the bowlders are firmly held by 

 the iron cement and sand, which serve as a matrix in which the 

 bowlders are imbedded; 

 when the latter weather 

 out their shape is pre- 

 served in the matrix. 

 While some of the 

 bowlders of this de- 

 posit may have been 

 brought here by float- 

 ing ice, it is probable 

 that most of the deposit 

 was left here by the 

 pre- Wisconsin ice sheet 

 when it advanced south 

 of the river. The finer 

 materials of the drift, 



if they were ever present, have been carried away, leaving the 

 gravel and bowlders, which were subsequently cemented by the 

 iron of the surface waters. 



Fig. 6. — Bowlder bed on the Missouri River 

 near mouth of Tobacco Garden Creek, McKenzie 

 County. 



MORAINE OF THE PRE-WISCONSIN DRIFT 



Mention has been made on a previous page of the moraines 

 of the Little Heart River Basin, and in McKenzie County a much 

 more extensive moraine of the pre-Wlsconsin drift forms a promi- 

 nent topographic feature of the region. It lies in the northeastern 

 part of the county, east of Tobacco Garden Creek, where it extends 

 on the upland from the edge of the Missouri Valley bluffs north 



