ANNUAL REPORT FOR 1874. 47 



range of ore beds extending eastward from Black River Falls ; a very 

 important question that might be determined, by the explorations 

 thus to be made. 



Before commencing the field-work of the season, Prof. Irving pre- 

 pared the supplementary report herewith submitted, embracing de- 

 tails of results attained in 1873, which, for want of time could not, as 

 before stated, be included in his general report for that year, now de- 

 posited in the office of the secretary of state. This supplementary 

 report, covering seventy-four pages of manuscript, with several maps, 

 diagrams and sections, will be found to contain much additional mat- 

 ter relating to the geology of Douglas, Bayfield and Ashland counties. 



The rocks in this part of the state are referred to five different per- 

 iods, as follows: 



1st. Laurentian Granite, etc. 



2d. Huronian Iron-bearing series. 



3d. Copper-bearing rocks. 



4th. Potsdam sandstone. 



5th. Quaternary Drift, etc. 



Many facts and arguments are adduced to show that this is the 

 proper order of arrangement, and ample details are given, so that geo- 

 logists may judge of the correctness of these views. 



Prof. Irving has been able to show the existence of a synclinal axis 

 extending in a southwesterly direction, through these counties, being 

 the westward inland extension of the great trough between Keweenaw 

 Point and Isle Royale, occupied mostly by the waters of Lake Super- 

 ior. We thus have a more clear understanding of the different direc- 

 tions assumed by the dip of the rocks at different localities, and are 

 brought to a knowledge of one of those grand movements in the re- 

 mote past, by which the solid rocks have been folded, contorted, and 

 lifted to their present complicated positions. To understand these 

 ancient disturbances of the strata is not only a matter of interest in, 

 speculative geology, but is also one of the greatest practical import- 

 ance to the miner and to all having occasion to deal with these rocks. 



It will be seen that the Copper-bearing rocks are Pre-Silurian, 

 though not as old as the Huronian. Prof. Irving's conclusions on 

 this point are that: 



1st. " The beds of the Copper-bearing series and those of the Huro- 

 nian were once spread horizontally over one another, including the 

 whole series of tilted sandstone on the Montreal river; they were dis- 

 turbed by the same force, and received their present tilted positions at 

 the same time, as evinced by the entire conf ormability of the two series. 



