CHENGWATANA SERIES 331 



of strike of the easternmost eastward dipping exposures seen and meas- 

 ured on the Kettle river. Assuming that the dip of the first half be that 

 at Chengwatana, and of the remaining distance that" on the Kettle river, 

 section 15, township 40, range 20 west, namely, 50 degrees east, the total 

 thickness of the flows and conglomerates of the Snake river is nearly 

 20,000 feet. In view of the fact that nowhere in Douglas county, Wis- 

 consin, on the Kettle river, nor along the Snake has any evidence of fault- 

 ing been seen within the flows beyond the ordinary slickensides incident 

 to the upturning of such enormous masses of rock, this must be regarded 

 as a very conservative estimate of the thickness of the series. 



Again this thickness, taken in connection with the measurements shown 

 by Irving for the north shore of 22,000 feet ; the Keweenaw point succes- 

 sion of 25,000 feet for the lower division alone, and that at Maimaisne 

 promontory, 20,000 feet, is an easily conceivable amount ; yet for a dis- 

 trict so far away from lake Superior, it is certainly unexpected. 



PETROGRAPHY OF THE SERIES 



Structural characters. — The conglomerates require but a word of further 

 description. They have been described in several paragraphs stating 

 their salient field characters. They show here and there some evidence 

 of crushing ; slight faulting is rarely seen. The compacting of the rock 

 until the finer particles or matrix of the pebbles begin to assume a crys- 

 talline aspect, as shown in the Keweenawan conglomerates farther north, 

 is nowhere detected. Veins are rather rare, and when seen are not more 

 than 2 or 3 inches wide. As a distinct rock, sandstones need not be 

 mentioned, since they are associated with the conglomerates simply as 

 local modifications of them. Ripple marks, cross-bedding, interpolated 

 boulder beds, etcetera, are among the usual structural features of the finer 

 layers. The breccias and tuffs of Taylors Falls present no special struct- 

 ural characters. The diabases occur in a series of lava flows possessing 

 the usual structural characters of such rock masses. In every part 

 great changes from the original condition of the rock are clearly in evi- 

 dence, and they seem to bear close relationship to the physical condition 

 of the lava beds. If badly shattered, the mineral condition is largely 

 changed ; if compact or fractured but slightly beyond the ordinary con- 

 version of a crystallizing mass into blocks, their sections exhibit a rock 

 of much freshness. A few of the flows exhibit a markedly concentric 

 weathering (see figure 2). Samples can be broken showing a dozen or 

 more concentric layers which peel off readily under the hammer. More 

 rarely, and yet among the freshest rocks anywhere seen, is an apparent 

 banding. When rocks are broken sufficiently deep, this proves to be 



