THE INTERPRETATION OF CERTAIN LEACHED GRAVEL 



DEPOSITS IN LOUISA AND WASHINGTON 



COUNTIES, IOWA. 



W. H. SCHOEWE. 



During the field season of 1917, the writer examined two ex- 

 posures of stratified sands and gravels, which, in age, may probably 

 be correlated with the close of the Nebraskan stage of glaciation and 

 with Af tonian times. 



The first of the two exposures, which are separated by about two 

 miles, is located in Washington county in the extreme southeast 

 corner of section 36, Iowa township. The other outcrop is found 

 in Louisa county in the northwest quarter of the southwest quarter 

 of section 8, Union township, Township 76 North, Range 5 West. 

 In both cases, the exposures are in banks of streams, the first form- 

 ing the north bluff of Davis creek, the second, the south wall of 

 Goose creek. The base of the two sections lies practically at the 

 level of Iowa river which is about one-eighth of a mile farther to 

 the east and which, according to barometric readings, is at 620 

 feet above sea level. 



As the two sections are very much alike, a detailed description 

 of but one will be given, and only the points of differences of the 

 other one will be brought out. The exposure to be described is the 

 one in Washington county at the location cited above. 



The section is as follows : 



Feet 



3. Light ash-colored drift 10 



2. Leached and oxidized sands and gravels 20 



1. Dark bluish calcareous drift; compact, unoxidized 

 and containing small pebbles 4 



Towards the base of the sand and gravel deposit, the gravels 

 predominate. The textural range of the gravels is rather high, the 

 pebbles varying from small fragments the size of a pea to pieces 

 several inches in diameter, the finer material, however, being in 

 excess. The gravels are cross-bedded. 



The sands which are highly oxidized and have a brownish color 

 are fairly fine and have a low textural range. In structure they are 

 highly contorted, dip at high angles, are cross-bedded and at places, 



