292 AUGUST F. FOERSTE 



Occasionally pebbles occur in the ripple-marked layers of lime- 

 stone. These pebbles usually are few in number and rarely are 

 sufficiently abundant even to suggest the term conglomerate. 

 They are more abundant at two horizons in the lower part of the 

 Liberty formation at the locality on Elk Run, east of Winchester, 

 Ohio, described by Prosser, than at any other localities known at 

 present in the Ordovician of Ohio, Indiana, and Kentucky, and there- 

 fore this locality has been chosen to present some of the features 

 characteristic of these pebbles. The pebbles are of two types. 



i. In one type the rock is very fine-grained, as though originat- 

 ing from a calcareous mud, and is frequently marked by worm- 

 burrows. There are also peculiar gouged-out markings, 3 or 4 mm. 

 wide, 60-100 mm. long, often 20 mm. deep at the center, curving 

 downward from the ends toward the center as though carved out 

 by some narrow gouge. Markings of this kind frequently connect 

 the two oblong or nearly circular terminals forming the peculiar 

 dumb-bell fossil called Arthraria. There are also gouged-out 

 markings only an inch in length (Fig. 6, pebble C). The surface 

 of these pebbles often is very irregularly rounded, as though the 

 rock had been soft at the time of formation of the pebbles. At 

 one horizon these pebbles frequently support small colonies of the 

 incrusting coral Protarea richmondensis (Fig. 5), 40-70 mm. in 

 width. In fact, twenty pebbles supporting Protarea richmondensis 

 were exposed along a narrow outcrop, a foot wide and scarcely 

 50 feet long, at the time of my last visit. Young specimens of 

 Streptelasma, presumably Streptelasma rusticum, 10-15 mm. in 

 length, occasionally occur, attached by their sides to the pebbles. 

 Three pebbles supporting young specimens of Streptelasma occurred 

 in the 50-foot length mentioned above. Incrusting growths of 

 Dermatostroma corrugata and of various thinly incrusting bryozoans 

 also occur occasionally. Since the incrusting growths follow the 

 irregular curvature of the pebbles, it is evident that the latter is 

 not due to subsequent erosion. In one specimen, thinly incrusting 

 bryozoans and growths of Stomatopora occur on the lower side of 

 the pebble, while thicker growths of Protarea richmondensis occur 

 on the upper surface, showing that the pebble had been turned 

 over at least once. 



