STRUCTURAL GEOLOGY 
167 
STRUCTURAL GEOLOGY 
Vanishing of Eastern Coal Seams in Indiana. In the early 
reports on the geology of the state frequent mention is made of 
some remarkable “cut-outs” in some of the large coal seams by 
Paleozoic rivers. A so-called Carbonic river that received special 
notice is that supposed to have existed in western Indiana, in the 
vicinity of Coxville, in Parke County. This old stream was 
thought to have excavated its channel in the top of the Pottsville 
series, and the evidence of its course to be indicated by a deeply 
filled valley penetrating the thick seam know as Coal III. 
In a recent special examination of this region the deposits occu¬ 
pying the line of the old alleged channel were found not to be 
filling a depression at all, but to form a distinct ridge. Coal III 
of the Alleghany series was demonstrated to thin out gradually to 
a knife-edge against the Coxville ridge. Over this ridge Coal 
III appears never to have accumulated in its full thickness. 
On the other hand the rider seam. Coal Ilia, was deposited in 
full thickness over the elevation and under normal conditions. 
The narrow belt of sandstone formerly thought to fill a deep 
erosion channel does not therefore cut out the great coal seam but 
represents a ridge in the ancient swamp basin which however 
appears to have disappeared before the deposition of the rider. 
The mining significance of this fact is of more than local inter¬ 
est, because of the circumstance that in so many localities through¬ 
out the coal fields old river channels have been described, whereas 
some of these alleged gorges are not such but perhaps even sand- 
dune formations instead. Instead of thick coal seams holding out 
in full development until abruptly terminated by erosion channels 
the pinching out is gradual. The disappearance is depositional 
rather than erosional in its character. Logan. 
Giant Bay Bar of Ancient Bonneville Lake. When Gilbert 
wrote his sumptuous history of ancient Lake Bonneville many of 
the most interesting and instructive features were quite inaccessible 
