106 GEOLOGY OF EASTERN "WISCONSIN. 



fold extension in the Upper Fox and Wisconsin river valleys, and in 

 the Rock river basin, and their attending slopes and ridges. 



If we descend to minor features, a large number of most interesting 

 phenomena will be presented. As these, however, are chiefly due to 

 erosion and to drift accumulations, they may most intelligently be 

 considered in connection with the drainage system and the glacial for- 

 mations. 



Elevations. The following elevations constitute a more specif- 

 ic class of topographical data. They will be of great value in 7nak- 

 ing estimates for Artesian wells, a subject which possesses very gieat 

 importance in this region, and in locating preliminary lines of rail- 

 road, in which respect they have already proved serviceable, and in vari 

 ous other ways. The elevations of railroad stations, and in manj 

 cases of intermediate points on the line, are those furnished me by 

 Dr. Lapham, fi-om the railroad surveys. To the same source, also, 1 

 am indebted for the altitudes of the Oconomowoc lakes, and some 

 other points. The elevations along the line of the proposed Chicago 

 and Midland railroad are from the survey of Mr. F. J. Starin, who 

 kindly placed the profiles at my service, which have proved of much 

 u"se in other ways. Elevations on the Peshtigo river were gener- 

 ously furnished by Mr. Paul "Wood, civil engineer of the Peshtigo 

 Company. A few have also been taken from other trustworthy 

 sources. These being the results of actual leveling, by competent en- 

 gineers, are a very close approximation to the actual elevations. The 

 remainder are the results of observations with aneroid barometers, 

 and are liable to more considerable errors, because the nature of the 

 iiistrument does not permit so great precision, and more especially 

 because of the fluctuations of the atmosphere, for which, in a series of 

 observations made in connection with and subordinate to ffeological 

 field work, it is impossible to make altogether accurate corrections. 

 A very large number of observations were made which are not thought 

 worthy of publication, because changes in the weather and other cir- 

 cumstances rendered them unreliable, and in using those given it will 

 be judicious to leave a liberal margin for variation due to changes in 

 the pressure of the atmosphere, which could not be detected. The la- 

 borious work of reducing the barometrical observations was chiefly 

 performed by Messrs, L. C. Wooster, G. D. Swezey, J. H. Chamber- 

 lin and C. S. Bacon. The elevations for Milwaukee county are the 

 results of a special and very full series of observations made by Chas. 

 Lapham, which the importance of that region, as a railroad center, 

 seemed to warrant. 



