118 Wisco7isin Academy of Sciences, Arts, and Letters. 



and fifty feet in height, towards the south, the horizontal layers 

 of sandstone are suddenly seen to change from their ordinary 

 position to a confused mass of broken layers, dipping in every 

 conceivable direction, and increasing in confusion as the trap 

 is approached, until, finally, the whole changes to a confused 

 breccia of mingled trap and sandstone fragments. This ap- 

 pearance is presented along both sides of the gorge, for a dis- 

 tance of 300 feet, and I am assured by my assistant, Mr. E. T. 

 Sweet, by whom all observations in Douglas county were 

 made, that it is certainly due to no mere surface displacement. 

 The same appearance is presented on one of the other north- 

 ward flowing streams in Douglas county, on a much diminish- 

 ed scale however, the undisturbed sandstones reachmg within 

 twenty feet of the trap. On all other of these streams, the 

 sandstones are undisturbed. The explanation which first sug- 

 gests itself to account for these disturbances is naturally, that 

 they were caused by the ejection of the traps through the al- 

 ready formed sandstones. In answer to this it may be said 

 that it is very difficult to see how just such a disturbance as 

 this could have been caused in this way, the sandstones pre- 

 senting no appearance of baking or other indication of heat, 

 but seeming rather to have been crushed by a pressure from the 

 south. Next the trap it is crushed to a confused mass, a little 

 further a few layers of sandstone become distinguishable, still 

 further these are all distinct but broken and pitching in every 

 direction, and finally they grade into regular unbroken hori- 

 zontal layers. It may also be said that the proofs already 

 given of the greater age of the copper bearing rocks, as com- 

 pared with the horizontal sandstones are so strong as to neces- 

 sitate some explanation of these disturbances other than the 

 one just mentioned. The only one that lean offer, is this ; 

 the traps being deep seated are, as it were, independent of the 

 more superficial sandstones, and would, if impelled to move by 

 any force, move independently of them. Now a very slight 

 movement of the traps northward against the sandstones would 



