622 W. H. TWENHOFEL AND F. T. THWAITES 



developed a gently rounded, discontinuously terraced topography. 

 Along the deeper valleys, in such places where the overlying 

 formation has not been completely removed, the upper strata of the 

 Dresbach rise from steep slopes to form coalescing tower-like cliffs 

 or conical buttes. 



Characteristics. — The exposed strata of the Dresbach consist of 

 poorly cemented quartz sandstones of which the grains are clean 

 and well rounded. In most of the beds the assortment is extremely 

 good. Interlaminated with the exposed sandstones are thin lenses 

 (up to about a centimeter in thickness) of green sandy shale. Well 

 records show the presence in the unexposed strata of greenish, 

 bluish, and reddish shale. Most of these occur about 450 feet 

 below the top of the Dresbach and may represent a part of the 

 Eau Claire formation. The sands are generally poorly cemented, 

 and very few layers are sufficiently firm for use in construction. 

 The colors vary from gray to yellow. "Iron rocks "^ — sands 

 cemented by hydrous iron oxide — are locally present in considerable 

 abundance, but are not characteristic of any horizon. 



The strata are not continuous for long distances, and with the 

 exception of worm-perforated beds, which are prominent in the 

 upper horizons, it has not been found possible to identify any 

 portion beyond the limits of a single exposure. In the field these 

 upper strata were known as the "wormstones." Cross-lamination 

 at variable inclinations with variable directions is present in nearly 

 every outcrop. The fore-sets are generally short, 5 to 6 feet being 

 the average maximum, but in an outlier near the village of Rock- 

 land there are fore-sets at angles of 15° to 20° which exceed 50 feet 

 in length. The inclination of the long fore-set cross-lamination at 

 Rockland is nearly due east. In a number of cases the cross- 

 lamination has the appearance of having been produced by wind 

 deposition. The nature of the Dresbach sediments was not 

 favorable for the development of mud cracks, but such are present 

 just east of Rockland in a horizon about 100 feet below the top of 

 the formation. 



The thickness of the exposed Dresbach is about 300 feet. Well 

 records show that from 590 to 615 feet are present from the base 

 of the Franconia formation to the pre-Cambrian floor. 



