CRITERIA or GLACIATED STONES 459 



sons g-lacial striation never partakes of the scliistose structure subparallel 

 to faulted surfaces whose motion has taken place under earth pressures. 

 In the case of glacial striation tlie stria' are normally single and those 

 on the movable rock fragment take diverse directions owing to the fre- 

 quently changed attitude of the fragment. Only in the case of the rock- 

 fioor or of large blocks lying at the side of the glacier do striae normally 

 develop in parallel groups, and in these instances the striae retain the 

 character of single successive scratches made by passing rock particles 

 held in the moving ice. 



Stki.e of THE Caney Shale Pebbles 



The striae and scratches on the boulders and pebbles in the Caney 

 shales are characteristically in groups of parallel striated grooves, in 

 which the intervening ridges are ribs the counterpart of the grooves in 

 appearance. A sort of flowage structure or cleaA age pervades the struc- 

 ture of the rock for a slight depth, showing that the striation took place 

 under conditions of great pressure, as in deep faulting with slickensides. 



In the case of some striated pebbles fragments of a different rock 

 remain in contact with the pebbles at the end of a surface of gliding and 

 striation, showing that the striation has been accomplished by rocks in 

 motion within the shale body. 



The surface of some of the limestone blocks displays a flowage contour 

 like that of clay under pressure. All the phenomena of striation and 

 flowage of the rock fragments in the Talihina cut coincide with the con- 

 tortion and slickensiding of the Caney shales at this locality in suggest- 

 ing the conclusion that the striae on the pebbles and boulders are an 

 effect of interstitial motion and displacement subsequent to the deposi- 

 tion of the Caney shale. An ironstone concretion formed in the con- 

 torted shales displayed the broad striated grooves such as are displayed 

 on the limestone boulders and pebbles (see figure 1, plate 23). 



Comments of Ulrich 



In commenting on my verbal communication before the Society, 

 Doctor Ulrich made the following pertinent statement concerning the 

 occurrence of striated pebbles in the Caney shales far south of the crushed 

 beds near the Choctaw fault : 



"The best of the many striated boulders found by Taff and luyscll" wjis foiuul 

 in the middle portion of a gently folded structural canoe far to the south of 

 the Choctaw fault. The boulder is of flinty chert, its outer surface rather soft 

 and partially decayed to a depth of one-fourth imh or so. The strise are deep, 

 though confined to the relatively soft outer shell, and the edges of the grooves 

 raisecl as though plowed in a plnstlce mass; and yet the Inclosing shale Is 



