A Strati graphical Study 
145 
Black Hand Formation. This horizon of rocks overlying the 
Cuyahoga is generally called a conglomerate. The conglomerate 
phase is indeed remarkably developed in many localities; on the 
other hand the formation consists locally of fine sand and even of 
argillaceous sands. From the standpoint of methods of sedimen- 
tation the striking feature of the Black Hand is its thickness (fig. 
13). We note, not infrequently, ledges often about 100 feet thick 
where it shows very little irregularity in texture. This constancy 
of shallow water or of littoral sediments implies a sustained rela- 
tionship of land and water brought about through the rate of 
deposition balancing the rate of land subsidence or of transgres- 
sion by the sea. Where, however, we find this formation inter- 
rupted vertically by beds somewhat coarse and often conglomeratic 
there is evidence of more vigorous erosion, or of tidal assortment 
combined with current scour, resulting in the localization of 
coarser deposits. Accordingly the conglomerate beds of the Black 
Hand are not consistent in horizontal development. For this 
reason we are inclined to favor the wave and current rather than 
the stream-erosion explanation for these coarser beds. 
The Logan Formation. This formation consists of sandstone, 
somewhat clayey in character, with now and then a thin layer of 
shaly sediments. The prevailing condition of sedimentation dur- 
ing this period is certainly not clear. The irregularity of the for- 
mation in horizontal extension, however, gives some suggestion. 
Furthermore, the general thickness of its beds leads to the same 
conclusion, namely, a transgressing sea following up rivers already 
mature in their drainage-cycle-position, with the rate of deposition 
lagging considerably behind the rate of transgression. The gen- 
eral absence of mud deposits and the fine texture of the sandstone 
in this formation both indicate a nearby source of sediments, 
presumably the working over of those last developed and of con- 
tinental sediments. Further evidence leading to this same conclu- 
sion is found in Conglomerate H, a persistent coarse horizon 
marking the boundary line between the Black Hand and the Logan. 
This conglomerate is widespread but not thick, its maximum 
depth usually being less than two feet. This relationship is sug- 
gestive of transgressive deposits marking a slow growth of a sea 
over the land in the gradually deepening of which water-body the 
Logan sandstones were laid down. 
The Pottsville Formation. The Sharon member of this forma- 
