ANNUAL REPORT FOR 1874. 



51 



must be deemed one of no inconsiderable interest, being the first in- 

 dication of the existence of these metals (uncombined) in the central 

 or soutbarn part of the state. Whether they exist at this place in 

 quantity sufficient to be profitably mined can only be determined by 

 sinking a shaft to the depth indicated. The copper-bearing rock was 

 exceedingly hard, and had a depth of eighteen feet. Until we know 

 the dip of this rock, it will be impossible to ascertain its real thick- 

 ness ; if the stratum lies horizontally (which is not very probable), it 

 has a thickness of eighteen feet; if it has a dip of 45° or more, its 

 thickness is only thirteen feet or less. It is not improbable that 

 when the proper trend of these rocks can be found, a search in the 

 right places may lead to further discoveries of importance. The top 

 of this well is 347 feet above Lake Michigan; Archaean rocks were 

 reached at 118 feet below; total depth of the well (December, 1874) 

 840 feet. 



One of the first results of Prof. Irving's survey of Dane county 

 was the identification of a hitherto unrecognized layer of sandstone, 

 far down in what has been classed as Lower Magnesiaa limestone; 

 to this, in accordance with the custom of geologists, he has given the 

 local name of "Madison Sandstone." It is much used in and about 

 Madison as a building stone. That portion of the Calciferous or 

 Lower Magnesian limestone series lying below the Madison Sand- 

 stone, and down to the Potsdam, forms the immediate shore of Lake 

 Mendota (4th lake), and has with much propriety been named the 

 " Mendota Limestone " in the report. This explains some anamolouS 

 sections heretofore made, and introduces two new names into the local 

 geological nomenclature. 



We thus find additional resemblance between the formations in 

 Wisconsin and those in Missouri, where Prof. G. G. Swallow long ago 

 recognized, and arranged under the head of " Calciferous sandstone 

 or Magnesian limestone series," seven different members, which may 

 now be parallelized with oiir strata as follows: 



MISSOnHI. ^1800118117. 



First Limestone, 190 feet. BufF Limestone, 50 feet. 



Saccharoidal Sandstone, 125 feet. St. Peters Sandstone, 100 feet. 



Second Limestone, 230 feet. Main Beds, 80 feet. 



Second Sandstone, 70 feet. Wanting. 



Third Limestone, 350 feet. Wanting. 



Tliird Sandstone, 50 feet. Madison Sandstone, 35 feet, 



rourth. Limestone, 300 feet. Mendota Limestone, 30 feet. 



Potsdam Sandstone. Potsdam Sandstone. 



Peof. T. C. Chambeelin's Paety. — Before entering upon the field 

 work, Prof. Chamberlin completed his report of the work done in 



