Structure of the Eastern Alps. 327 



when it is stated, that a line drawn directly transverse to the strike of the beds, 

 from the point where they set on with a regular, northern dip, to the hills on 

 the Ach immediately behind Bregenz, is not less than six miles in length ; 

 and that along the whole of this line the average inclination of the beds is not 

 less than 20° or 25°. 



Pursuing the same line of section across the river Ach, which here empties 

 itself into the Lake of Constance, we find an escarpment several hundred 

 feet high, composed of brownish red, coarse conglomerate, alternating with a 

 reddish, cjuartzose sandstone, so fine in parts as to resemble grauwacke ; but in 

 other and higher alternations with the conglomerate, it passes into a soft, yel- 

 lowish and brown, micaceous sandstone. In the upper beds of the cliff on 

 which the castle stands, are some large Ostreee, and fragments of smaller 

 and more destructible shells. The conglomerate is chiefly made up of the 

 detritus of Alpine limestone, and its higher subdivisions begin to alternate 

 with sandstone beds of a slaty character : behind the town of Bregenz it 

 passes under a well-defined molasse, undistinguishable from that which 

 abounds so much in the lower parts of this sectional line, as well as from the 

 77wlosse of Rheineck and Roshach on the opposite side of the valley of the 

 Rhine. 



This Bregenz inolasse is largely quarried, and is a good example of that 

 fine, greenish, micaceous sandstone which appears in all the public buildings 

 around the Lake of Constance. Certain varieties of it are used for whetstones 

 or grindstones ; a fact, however, from which alone no inference can be draw n 

 respecting the age of the deposit, inasmuch as both the secondary and tertiary, 

 greenish sandstones of the Alps, are occasionally used for these purposes. In 

 the upper and less coherent beds of these quarries, are imperfect casts of 

 bivalves : much finely comminuted, black, carbonaceous matter is also dissemi- 

 nated, especially in the planes of separation of the more slaty masses. This 

 molasse is again overlaid by a vast thickness of conglomerate, like that of the 

 castle-hill, with a reddish brown, siliceous cement, and with imbedded pebbles 

 varying from one to eight inches in diameter. Still higher these conglome- 

 rates alternate with yellowish, sandy grits, which are marked by red and green 

 spots and concretionary, argillaceous blotches. Then follow sandy marls and 

 thin-bedded sandstones, again surmounted by strong courses of conglomerate : 

 and this system is continued along the hills for several thousand feet, being- 

 distinguished in the ascending order by some subordinate beds of grit of a 

 brick-red colour ; and by others of green and grey colours. 



The rugged outline of this portion of the ridge, is due to the structure we 

 have just described. For the elements have washed away many masses of 



