C. B. Keyes — Bedrock Sandstone of Marion Co., Iowa. 273 



Akt. XXX. — The Bedrock Sandstone of Marion County, 

 Iowa ; by Charles K. Keyes. 



[Read before the Iowa Academy of Sciences, September 5, 1890.] 



The sandstone of Redrock, in Marion County, Iowa, has 

 recently come into prominence as a building stone ; and is 

 now used more or less extensively throughout the State for 

 the better class of architectural work. Long ago this rock 

 was utilized in various structures at DesMoines and elsewhere, 

 but the method of obtaining it, by blasting, shattered the stone 

 so as to render it almost worthless for building purposes. It 

 soon fell into disrepute and for more than thirty years has not 

 been used except for unimportant local masonry. Recently 

 extensive steam sawing apparatus has been brought in and the 

 stone removed in huge blocks before reduction by further saw- 

 ing to sizes required. In this way the sandstone is not injured 

 as when the blasting method was in vogue. The resistance to 

 crushing power of the better portions of the rock is now con- 

 sidered to be nearly equal to any in the country. 



The Redrock sandstone has long attracted popular attention. 

 The bright vermillion cliffs rise to a height of one hundred to 

 one hundred and fifty feet above the water surface of the Des- 

 Moines river. The red coloration of the rock is, however, local, 

 merging laterally and downward into a yellow or buff color. 

 The formation has a known geographic extent of at least 

 twenty miles and probably stretches out much farther. At 

 Redrock cliff the stone is, for the most part, massive ; but 

 rather soft and thin-bedded above. At this place it is a very 

 fine grained and homogeneous sandrock, some portions even 

 affording excellent material for grindstones. But southwest- 

 ward, and at Elk bluff two miles below, the sandstone passes 

 into a fine-grained, ferruginous conglomerate. The dip is 

 everywhere to the south and west ; and, at a short distance 

 above the quarry just alluded to, the inclination is very con- 

 siderable. A mile beyond, the sandstone has disappeared 

 completely and the section shows only shales and clays. The 

 space between the latter exposure and the last known outcrop 

 of the sandstone is perhaps half a mile, the interval being hid- 

 den by Quaternary deposits down to the water-level. The 

 abrupt change in the lithological characters of the rocks in so 

 short a distance has been mentioned by Owen* and Worthen,f 

 but the true explanation is entirely different from the suppo- 

 sitions of those writers. 



At Redrock quarry the strata overlying the sandstone are 

 disclosed as shown in figure 1, the horizontal and vertical scales 

 * Geology Minn., Iowa and Wise, 1854. f Geol. Iowa, 1858. 



