126 ILLINOIS ACADEMY OF SCIENCE 



bed is uniformly, in all localities where measurements have 

 been possible, from 20 to 25 feet above the Yankeetown chert. 

 The exact thickness of the red bed itself, however, cannot 

 often be observed because of the weathering and slumping 

 of the material over the underlying strata, but where the 

 interval immediately above the Yankeetown has best been 

 seen, a series of bluish calcareous shales with plates of lime- 

 stone extends for several feet above the chert. The actual 

 thickness of the red bed is probably about 12 or 15 feet- in 

 the natural outcrops which have been observed, and this 

 thickness is confirmed by the records of several dug wells 

 which have penetrated the stratum. When encountered in 

 well digging the bed is very hard and tough and can be ex- 

 cavated only by the aid of blasting, but when exposed to the 

 weather it rapidly breaks down into a fine red mud. On 

 freshly exposed surfaces in creek banks this red clay first 

 clumbles into angular fragments, usually a fraction of an 

 inch in maximum dimension, and finally breaks down into 

 a fine red mud. The origin of such a bed as has been des- 

 cribed, persistent as it is through a distance of at least 

 30 miles in the Waterloo and Renault quadrangles, is not 

 clear. In its physical characters it closely simulates certain 

 beds of red residual clays, but such an origin for this stra- 

 tum, occurring as it does conformably in the midst of typical 

 marine sediments, seems to be out of the question. One of 

 the best points to observe this meml)er of the Paint Creek 

 formation, as well as the higher members of the same forma- 

 tion, is the valley of the tributary of Paint Creek, entering 

 from the south, situated about one and one-fourth miles 

 southwest of the village of Ames. 



The higher, more calcareous members of the Paint 

 Creek formation, shaly below and passing into firmer lime- 

 stone beds above, are well exposed in many localities in the 

 \\^aterloo and Renault quadrangles. In some localities under- 

 lain by the limestones of the formation, numerous sink holes 

 are developed in the topography, such a condition being pres- 

 ent on the divide immediately west of Ames. 



5. Ruma Formation, 



General characters. Succeeding the upper limestone mem- 

 ber of the Paint Creek formation, is a series of shales 

 the sandstones, rarely if ever more than 40 or 50 feet in 

 thickness. The shales usually predominate, but in all lo- 

 calities where the formation is well exposed, there are im- 

 portant, thin-bedded sandstone layers and some arenaceous 

 shales near the middle of the formation. The more shaly 

 beds are in almost all localities conspicuously variegated, being 

 blue, reddish and purple in color, not unlike some of the shale 



