258 GEOLOGY OF EASTERN WISCONSIN. 



In general, as seen in outcrops in eastern Wisconsin, they are 

 neither very coarse nor very fine, but range through the medium 

 varieties. Near the base of the formation a very coarse grained 

 sandstone occurs, but it is not known to outcrop in the district. In 

 some cases these grains are embedded in more finely comminuted 

 silicious powder, doubtless worn from the grains themselves, so that 

 the rock possesses considerable compactness, but only a small degree 

 of cohesive power. In other cases, the filling between the grains is a 

 clayey material, or a green earth, forming an argillaceous sandstone, 

 or one of the varieties of greensand. 



Still again, and very commonly, the grains of sand are firmly ce- 

 mented by calcareous or ferruginous matter. In many cases this is 

 not so much a filling of the spaces between the grains as it is a coat- 

 ing of the grains themselves, by which they are firmly bound to- 

 gether. It is this variety that furnishes the most serviceable building 

 material. 



As a result of these facts, the formation presents several varieties 

 of sandstone, which may be known respectively as the calcareous, the 

 non-calcareous, the argillaceous, the ferruginous, and the green sand. 

 Sandstone entirely free from calcareous matter is rare in this forma- 

 tion in eastern Wisconsin. 



Whether we examine outcropping ledges, artificial exposures, or the 

 drillings of Artesian wells, the presence of more or less of lime is 

 usually indicated, except in the lowest stratum of the formation. As 

 has been before remarked, the waters issuing from this formation 

 usually contain a small percentage of lime salts. Whether they de- 

 rive their calcareous burden from the sandstone, or, on the contrary, 

 are the sources in part of the lime in it, having obtained it originally 

 from the limestone above and yielded it to the sandstone in passing 

 through it, may be a matter of doubt, in some cases, but a portion of 

 the lime was undoubtedly deposited at the same time with the sand. 



All of the non-calcareous sandstones, observed in the district 

 under consideration, crumble so easily as to be of little industrial 

 importance except as a source of sand, and as they form a sterile soil, 

 their rarity may be considered a matter of good fortune. 



In the argillaceous class, the clayey material sometimes becomes 

 so abundant as to render the rock shaly, and in some cases it so far 

 predominates that the rock is known as a shale, rather than a sand- 

 stone. These argillaceous layers are usually impervious to water, 

 and demonstrate their utility by giving origin to valuable springs. 



There are two classes of green sand, one, which consists of grains 

 of quartz colored by some substance iron in those cases which I 



