In addition to these observations, I have pursued my inves- 

 tigations upon the Potsdam sandstone and the succeeding for- 

 mations ; which, with the previous researches will be fully 

 detailed in the final report. 



The investigations upon the rocks of the Niagara group 

 and associated strata, have likewise been continued, and I have 

 arrived at certain results fortified by the occurrence of numer- 

 ous fossils which lead me to conclude that the Racine lime- 

 stone, mentioned in a former report, is the upper member of 

 the Niagara group, while the heavy bedded mass below is but 

 the expansion of the limestones of the Clinton group. This 

 opinion in regard to the last named rock I advanced some 

 years since, but having until this time no satisfactory evidence 

 of the occurrence of the higher member of the Niagara group, 

 I had been forced to admit that the whole had merged in one 

 great calcareous mass. This part of the subject will be more 

 fully discussed in my next report. 



I have had an assistant, Mr. T. J. Hale, in the field from 

 the bes;innin£ of Julv to the end of the season. His labors 

 have been directed to tracing in detail the outcrops of the for- 

 mations on the east of the central axis, and in collecting fos- 

 sils. He has also collected economic materials and soils for 

 the other departments of the survey. During the latter part 

 of the season Mr. Hale has been employed in the lead region 

 to complete the collection of fossils necessary for the palaeon- 

 tology of that report, which is now being prepared. 



Under the supplementary law of last session, relating to the 

 geology of the State, I was directed to make a contract with 

 Prof. J. D. Whitney for the completion of the map and report 

 of the lead region ; and with Col. Charles Whittlesey for the 

 continuation of his work in the Lake Superior region. In ac- 

 cordance with this law, and with the approval of your Excel- 

 lency, these contracts were made, and the work continued. 

 Since that time Mr. Whitney has completed his report and 

 maps, which, by the terms of the act referred to, have been 

 placed in the engraver's hands, and I hope to send finished 

 copies of one of them with this report. The other map will 

 require yet some time for its campletion. I have also made 

 arrangements for, and progress in, the work pertaining to 

 other illustrations for this report. The report of Mr. Whittle- 

 sey will soon be completed and placed in my hands, and will 

 be subject to your direction. 



Mr. Hale will communicate to me a detailed report upon his 

 local examinations, which may be incorporated in my final 

 report. 



