254 a. m. purdue cave-sandstone deposits of the ozarks 



Shape and size of Sandstone Masses 



In shape these sandstone masses vary from those of about equal dimen- 

 sions in all directions to those whose length is much greater than their 

 thickness. In some cases a mass will stand alone on the hillsides, and in 

 other cases several occur closely associated, but usually at different levels. 

 Frequently they are arched at the l^ase when the material beneath is 

 usually weathered out, sometimes leaving a cavern large enough to protect 

 stock during stormy weather. This basal arching is so common as to 

 almost be a characteristic of the masses (see figures 1 and 2, plate 6). 



Character of the Sandstone 



The sandstone composing the masses is saccharoidal and to all appear- 

 ance is the same as the Saint Peter of this region. It is made up of 

 medium sized, well rounded grains, so loosely bound together that fre- 

 quently they crumble in the fingers. Beneath the blows of the hammer 

 it is so friable that securing a hand specimen is a difficult matter. It is 

 always of the same nature in the different masses and uniform throughout 

 the same mass. No argillaceous material occurs in it. No stratification 

 planes are visible, but often there are poorly developed cleavage planes 

 standing perpendicular or at a high angle. Angular fragments of chert 

 like that in the surrounding limestone are common in the sandstone, as 

 also are blocks of angular limestone. These limestone blocks often are 

 so large as to make it impossible for them to have been deposited by 

 water. Careful search for conglomeratic material in the sand never re- 

 vealed any that I could be confident was such. Loose material like that 

 found on the floors of the caves may sometimes be seen beneath the sand, 

 and in one case old stalagmitic material was found. In another case sev- 

 eral feet of the outer surface of one of the masses were distinctly slicken- 

 sided, the markings being vertical. In this case the inclosing limestone 

 was very slightly arched beneath the sandstone mass, but the slight folding 

 could not have caused the slickensides. There was no faulting of the 

 inclosing limestone. In some cases the surface of the sand is weathered 

 so as to give it a distinctly mammillary appearance — a thing which the 

 writer does not attempt to explain. 



EeASONS FOR CONSIDERING THE SanD MasSES CavE DEPOSITS 



The reasons for considering the sand masses cave . deposits seem to the 

 writer to be conclusive and are as follows : 



1. The abrupt manner in which the limestone beds usually abut against 

 the sandstone masses, 



