772 JESSE E. HYDE 



It is possible that a fourth member should be recognized. 

 E. B. Andrews in 1878 proposed that certain beds at the top of the 

 Logan formation at Rushville be designated the Rushville^ group. 

 There are there shown 22^ feet of rather soft argillaceous shales, 

 gray or red in color, of a type quite different from the bulk of the 

 sandy sediments that compose the Logan, and a pink crinoidal sandy 

 limestone one foot thick. These beds are stratigraphically much 

 higher than those which usually form the top of the Logan. This 

 is because the pre-Pennsylvanian erosion surface here stands, 

 relative to the beds it cuts, much higher than in most places. In 

 addition, these beds were stated by Whitfield to show certain 

 faunal peculiarities that, if verified, will distinguish them from the 

 remainder of the Logan. The fauna has been extensively collected 

 but no statement can be made as yet. 



Although the three members listed above are found throughout 

 the length of the Logan belt from central Ohio to the Ohio River, 

 they are not present throughout its entire breadth, as is shown 

 by the map (see Part I) of the known distribution of the Allens- 

 ville member. In Scioto County the western limit of this bed is 

 quite definitely known. In Pike and Ross counties its absence from 

 the western half of the Logan belt is not demonstrated because of 

 covered slopes and absence of outcrops, but such absence is very 

 strongly suspected. It is in part on the presence of this member 

 that the subdivision depends. The upper member is occasionally 

 absent because of erosion prior to the deposition of the Pennsyi- 

 vanian or Coal Measures; yet more rarely all three have been 

 removed. 



The lower and upper members are fine-grained sandstone and 

 shale deposits, the result of quiet, uniform conditions; the Allens- 

 ville bed is a very coarse sandstone, or perhaps it would better 

 be called a fine pebble bed, the result of an interval of contraction 

 of the basin. The whole is marine throughout, although faunal 

 remains may be rare. 



The Byer member. — This is usually a fine-grained sandstone. 

 Its beds are seldom over 18 inches thick and may tend to split 

 up into thinner beds. In southern Ohio, and especially in the more 



^ Am. Jour. Sci., 3d ser., XVIII C1879), 137. 



