136 Wisconsin Academy of Sciences, Arts, and Letters. 



tion of the conglomerate ; not to speak of the time sufficient to 

 erase all signs of an anticlinal. 



4th. The occurrence of horizontal sandstones resting unconform- 

 aUy on the flanks of the tilted strata. This last is, of course, 

 absolutely conclusive as to the north range, but lest it might 

 be claimed that the two are independent, I have given the 

 others. 



Mr, Winchell argues that, since Mr. Hall states that the 

 fossils I have mentioned as occurring in the conglomerate are 

 restricted to the Middle Potsdam, either this statement must 

 be untrue or the quartzite must be the downward continuation 

 of this formation. This argument, however, loses all force 

 when we regard these ranges as high ridges in the Potsdam 

 seas, never having been entirely covered by these seas, but 

 having merely had the new sandstones and conglomerates 

 deposited about their flanks. The place where these fossils 

 were found must be at least 200 feet above the base of the sand- 

 stones of the surrounding country. A single glance at Dr. 

 Lapham's geological map of Wisconsin will show this. The 

 conglomerate is by no means necessarily the hase of the Pots- 

 dam because it rests immediately on Huronian or Laurentian 



rocks. 



In the final report of Mr. Hall already referred to, he men- 

 tions a low hill north of Baraboo, in which the middle of the 

 hill is quartzite, and the flanks conglomerate and sandstones 

 graduating upward into calcareo-sandy layers, without giving 

 any further explanation. This statement, before somewhat 

 unintelligible to me, now throws further light on my own 

 results. 



To my mind these ridges were unquestionably islands in the 

 Potsdam sea, and a more beautiful illustration than is furnished 

 by the sandstones and conglomerates of wave action on a rocky 

 coast, can hardly be imagined. 



There are many very interesting details of structure in these 

 ridges which would repay thorough study. The points pre- 



