CLINTON FORMATION NEAR DUB U QUE 121 



AN OUTLIER OF THE SO-OALLED CLINTON FORMA- 

 TION IN DUBUQUE COUNTY, IOWA. 



JESSE V. HOWELL. 



During the summer of 1914 a considerable amount of grading 

 was done at the forks of the road on the west side of Lora Hill, 

 seven miles west of Dubuque. As a result of this work there 

 was exposed along the road a band of peculiar reddish clay from 

 one to two feet in thickness, underlain by the characteristic 

 gray-green, plastic clay-shales of the Upper Maquoketa forma- 

 tion. The red clay is much less plastic than the underlying 

 green shales, but is remarkable chiefly for the fact that it is com- 

 posed largely of iron oxide and contains great numbers of small, 

 rounded concretions or oolites. Also imbedded in this deep red 

 clay are: a. numerous pebbles of smooth, polished chert, b. 

 rounded fragments of indurated material similar to that of the 

 clay, and c. rounded fragments of slightly iron stained shale. 



The fragments belonging to the second class are crowded with 

 oolites, but contain no fossils. Weathering has so softened the 

 material of both oolites and matrix that it is not possible to polish 

 the fragments for satisfactory microscopic study. 



"When examined under the low power of the microscope the 

 oolites are seen to possess the same concretionary structure which 

 characterizes similar bodies 1 in the "Clinton" formation of Wis- 

 consin and the true Clinton ore of the eastern states. The in- 

 dividual layers or coatings separate rather readily, exposing, 

 usually, a more or less definite nucleus. Many of the oolites on 

 being dried, show somewhat glazed surfaces, especially after re- 

 moval of the outer layers. 



Particularly in those portions of the clay near the contact with 

 the unstained green shale, the red clay contains many fossils. 

 All the forms appear to be of Ordovician age, and it seems prob- 

 able that they come from the green shale, for a majority of the 

 specimens are not replaced by iron. Two individuals, appar- 

 ently sponges, are composed largely of iron oxide, but the struc- 

 ture has been so destroyed by weathering that their identity is 

 not certain. Most of the fossils are silicified and all of them 

 are broken and comminuted. 



