207 



Some convulsion of nature, a local upheaval and subsidence of the 

 earth's crust, was among the theories genei'ally accepted for a time, to 

 account for the false bedding of the ^A'abash Valley rocks. Prof. CoUett, 

 in 1872, was the first to offer an explanation more nearly in accord with 

 recent observations. Of a Delphi locality he writes: "'The Pentamerus 

 bed is an irregular deposit, variable in its mode of occuiTence and thick- 

 ness, evidently deposited by currents tiowing across irregularities in the 

 surface of the regularise deposited rocks below. It is generally found 

 thrown down upon or against these irregularities, and consequently ex- 

 hibits remarkable peculiarities of false bedding." But his theory does not 

 account for the uneven surface of the regularly deposited rocks. The most 

 obvious explanation is to suppose that they are due to erosion, and that 

 they indicate the upper surface of the lower member of an unconformity. 

 Especially must this be true Avhere the stratification of the stone, com- 

 prising the iri'egular surface, is found to be level and the layers of uni- 

 form thickness. Where the iri-egularity forming the axis or center of a 

 cone is composed of shale it is not impossible that it may have been 

 formed ^y currents. The effect of currents on the contour of a shale bed 

 was clearly demonstrated in an example of irregular bedding seen in the 

 quarry of Tames Lambert at South Wabash. Here an axis of shale had 

 been deposited between the quarry stone layers, which maintain a uni 

 form thickness while conforming to the irregular surface of the shale. 

 Near Lagro, at the Watson Briggs ravine, is a beautiful exixtsui'e on a 

 large scale of the picket rock passing over a central axis of a cement 

 shale with the dip in opposite directions. On the flanks of the axis the dip 

 changes from 20 to 12 degrees and the layers become horizontal as they 

 pass over the top. These exposures are supposed to show the primary 

 origin of the false bedding in nearly all cases, and especially so when the 

 distorted layers are of nearly uniform thickness. But in many cases other 

 phenomena are involved and the explanation is not so simple. Irregu- 

 larities of the underlying surface do not account for the brecciated con- 

 dition, changed physical characters and the nearly vertical planes of so- 

 called stratification. 



The brecciated character of the Indiana stone seems to have been 

 first pointed out by Prof. Orton in the eighth annual report of the United 

 States Geological Survey. Of the Ohio stone, with which he compares the 

 Indiana outcrop, he says: "The layers of limestone appear to have been 

 traversed by joints dividing them into cubical blocks of two or ten inches 



