BYBEE-MALOTT : THE FLOOD OF 1913 



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stone intercalated with shaley layers. The Knobstone is between 

 400 and 600 feet in thickness. The area of outcrop is from twenty- 

 five to thirty miles in width and extends from the Ohio River north- 

 ward through Floyd County, western Clark, eastern Washington, 

 western Scott, nearly the whole of Jackson, Brown, Morgan, Hen- 

 dricks, and Montgomery Counties, passing under the glacial drift 

 in Benton County. The topography of this region is the most 

 rugged of any in the State. The Knobstone rocks absorb water 

 readily, but being impervious, transmit it very poorly, so that these 

 rocks are readily shattered by freezing and thawing. The region 

 is weathered and eroded into steep-sided valleys, the bottoms of 

 which are from 200 to 400 feet below the general level of the land. 

 The topography of Brown County is a good example of these steep- 

 sided valleys. Since the elevation of the region is from 700 to 

 1,100 feet above the sea, it is known as the Central Highland. 

 The courses of both forks of White River are to the southwest 

 directly across the Knobstone region. The valleys are from two 

 to five miles in width and are bordered on either side by abrupt, 

 bluish bluffs, ranging from 150 to 250 feet in height. Typical 

 bluffs of this kind are to be found on the West Fork above Martins- 

 ville and on the East Fork at Brownstown and Sparksville. 



The Harrodsburg limestone which overlies the Knobstone, 

 is a coarsely crystalline, fossiliferous, hard, blue stone from 35 to 

 100 feet in thickness. Its outcrop is between a quarter of a mile 

 and three miles in width. The topography is very similar to that 

 of the succeeding formations. 



The Salem limestone overlies the Harrodsburg limestone. 

 It is a massive, oolitic, buff to bluish, fossiliferous limestone, known 

 over the United States as one of the best building stones. The 

 softness of the freshly quarried rock makes it very easily worked, 

 and upon exposure to the air it gets hard and durable. The thick- 

 ness of the Oolitic limestone varies from a few feet up to 90 f^t. 



The Mitchell limestone is a hard, fine grained fossiliferous, blue 

 stone, having a thickness ranging from a few feet up to, possibly, 

 250 feet. This limestone is easily soluble and is pitted over its en- 

 tire outcrop with sinks. The region of its outcrop is largely drained 

 by underground channels. It is in this formation that some of the 

 largest caves of the world are found. Some of the noted caves 

 found in the Mitchell limestone are Mammoth Cave of Kentucky, 

 and Wyandotte and Alarengo Caves of Crawford County, Indiana. 

 Lost River in Orange County is a typical underground stream for 

 thirteen miles of its length. Green River, Kentucky, drains ]\Iam- 



2—1424 



