JCXE 21, 1S95.] 



SCIENCE. 



en 



and the positions of the pieces slightly 

 changed, bnt not widely separated as they 

 would inevitably have been had the brec- 

 eiated masses been accumulated by wave 

 action on a seashore. The liAiJOthesis tliat 

 the brecciation and contortion were pro- 

 duced by undermining of the strata and by 

 subsequent crushing from the weight of the 

 superincumbent rock is inconsistent with 

 the facts. The lower members of the De- 

 vonian strata are undisturl)ed, and in the 

 central portion even the whole of Xo. 2 

 seems to be present and perfectly horizon- 

 tal and the breccia rests on it increasing 

 the thickness of the Devonian strata from 

 its normal 20 feet to 40 feet in the central 

 portion of the disturbance. 



In short, the only tlieory which will ex- 

 plain all the phenomena is that which has 

 been applied, in explanation of the manner 

 of formation of similar but vastly more 

 extended Devonian limestone breccias in 

 Iowa, viz.. by lateral pressure produced Ijy 

 the ' creep * or sliding on a sloping sea bot- 

 tom of the displaced strata immediately 

 after their deposition. 



From a study of the strike of the undu- 

 lations, displacements and other attendant 

 phenomena, it becomes evident that the 

 pressure was applied from the northeast. 

 The Devonian strata at present rise in that 

 direction at a rate not exceeding S or 10 

 feet per mile, and during the Devonian age 

 were doubtless still more nearly horizon- 

 tal. It is remarkable that so slight a slope 

 could have given rise to a sliding of a por- 

 tion of the sea bottom, but it is undoubtedly 

 the fact that, while the deposition of the De- 

 vonian strata had proceeded witliout in- 

 terruption to the top of the shaley limestone 

 Xo. 2, the upper 2 or 3 feet began to slide on 

 the underlying stratum. About the western 

 line of Stone count}' the resistance over- 

 came the weight of the ' creeping ' strata, 

 and the tension becoming too strong, at one 

 place certainly and perhaps at others not yet 



discovered, that they suildeidy gave waj', 

 were contorted, brecciated. forcwl forward 

 and hurled in boulder-like niasseson to other 

 undisturl>ed strata. 



Considering the intensity of the force and 

 the conditions under which it was applied, 

 it is surprising that the area of the disturb- 

 ance should be so small ; on the opposite 

 side of the valley, one-eighth of a mile dis- 

 tant, there is not the slightest sign of it, and 

 in the next valley, one-fourth of a mile south- 

 west from it. the Devonian strata are undis- 

 turbed. Its areal extent cannot be greater 

 than one-fourth square mile. 



The lithificatiou of the shaley limestone 

 was practically complete at the time of the 

 displacement, for the fragments are all 

 sharply angular and must then have been 

 very hard. And as the relation of the over- 

 lying strata shows that the period of the 

 disturbance immediately succeeded that of 

 deposition of Xo. 2, deposition and lithifica- 

 tion must have proceeded contemporane- 

 ously. 



The green shale, which is the upper mem- 

 ber of the Devonian in this region, thins 

 out in the hollows between the dome-shaped 

 prominences of the surface of the breccia, 

 and totally disappear over the higher por- 

 tions of the disturbed area. The points 

 where it is ab.seut are not now and never 

 were more than twenty feet higher than the 

 surrounding sea bottom, where tlie green 

 shale was deposited in very regular lami- 

 na?, without wave action. The areal dis- 

 tribution of tlie green shale is such as to 

 show that it was deposited in a compara- 

 tively small and shallow esturine basin, 

 connecting with the sea toward the south, 

 and supplied with fine sediment from the 

 land on tlie east and north. The limited 

 extent of this bodj- of water accounts for 

 the feebleness of its waves, which did not 

 affect the green shale at the depth of only 

 twenty feet around the elevated area formed 

 by the breccia. Tlie higher prominences 



