NIAGARA LIMESTONE. 337 



will be applicable in a general way to the formation at all points, and 

 will be of practical service, as some layers are valuable and others 

 comparative!} 7 worthless. It will, however, be impossible to readily 

 distinguish all these layers at every point. 



The lowest stratum consists of from four to ten feet of shaly, im- 

 pure limestone, usually of a yellowish gray, but sometimes of a 

 greenish hue. The beds, at some points, attain sufficient thickness 

 and soundness to be serviceable as building stone. At Iron Ridge, 

 this stratum either disappears or loses its characteristics. 



Upon this lies a stratum of hard, heavy-bedded magnesian lime- 

 stone, usually gray in color, and generally characterized by prominent 

 vertical fissures and obscure and distant bedding joints. It does not 

 make good quicklime, and is of comparatively little value as a build- 

 ing rock. It varies from six to twelve feet in thickness. The third 

 general stratum is composed of three parts, as found in most places. 

 The lower one consists of broken fragments of limestone imbedded 

 in a greenish, bluish or yellowish, marly clay. More or less of chert 

 is present. The middle portion consists of compact, sometimes 

 cherty limestone, in even beds, from four to fourteen inches thick, 

 and serviceable for building stone. The upper portion is a repetition 

 of the lower. The three portions are not to be distinguished, how- 

 ever, at all points. The chert is sometimes almost entirely wanting, 

 as in Oakfield, and sometimes is a very prominent feature, as in Ot- 

 tawa. The entire stratum varies from five to thirty-five feet in thick- 

 ness. In the town of Taycheedah, there occur at the bottom of this 

 stratum a few regular beds that are marked by an abundance of Stro- 

 matopora, very imperfectly preserved. They should probably be 

 grouped with the above, as Stromatopora extends into its layers. 

 This stratum is overlaid by an even bedded limestone, usually quite 

 hard, compact, fine grained, white or light gray, often nearly a pure 

 dolomite, and a valuable rock. At the same horizon, or just above it, 

 in Taycheedah, Empire, Ashippun, and less distinctly at some other 

 points, there occurs a reddish yellow, granular crystalline dolomite, 

 called by the workmen and residents " sandstone." It is, in fact, an 

 unusually pure dolomite, so that if the term is understood to imply 

 that the rock is silicious, it could scarcely be more erroneous, since 

 the amount of silica is not more than about one-fourth of one per 

 cent. It is, however, a fine example of calcareous sandrock. The 

 grains are chiefly minute crystals, that show no evidences of wearing 

 action, and have evidently not been disturbed since their crystalliza- 

 tion. The interstices between the crystals are to a considerable ex- 

 tent unfilled by any matrix, making the stone highly porous, and, in 

 Wis. SUR. 22 



