LOWER MAGNESIAN LIMESTONE. 273 



a few rods, consist of two classes, thin undulating beds and thick brecciatsd ones; the 

 two alternating, in a measure, with each other. The latter are very hard and crystalline 

 in texture. Some of the angular cavities that constitute the interspaces between the 

 fragments of the breccia are filled with calcite and pyrites, but most of them are empty, 

 giving the impression that the rock had been crushed. But this, with one or two other 

 similar cases, is exceptional. The breccias that are so common a feature in this lime- 



FIG. 28. 



1. Lower Magnesian Limestone. 2. St. Peters Sandstone. 3. Trenton Limestone. 



stone cannot, in my judgment, be satisfactorily explained by any form of crushing after 

 deposition. In this instance the undulatory nature of the thin beds, and the hardness 

 and crystalline character of the brecciated rock lend some plausibility to the idea of com- 

 pression, or forcible upheaval, as the cause of this apparent flexure of the Lower Magne- 

 sian strata. But we shall have occasion to consider a large mass of facts not in conso- 

 nance with such a view. 



The figure, which exhibits an east and west section, shows that the strata dip in both 

 those directions, and by following down the stream to the northward, they are seen to 

 slope rapidly in that direction also. To the south they are concealed, but judging from 

 analogy, they descend also in that direction within a short distance, thus forming n 

 dome supporting the Trenton strata above. 



The character of the sandstone, which will be considered more fully under its appro- 

 priate head, makes it evident that the sides of this dome were subject to the action of 

 the waves while the St. Peters sandstone was being deposited, demonstrating that 

 whatever cause produced the arch, acted before the sandstone was formed. 



In sections one of this town and thirty-six of the town north, the Lower Magnesian 

 and Trenton strata are found at the same level and very near each other, leaving no 

 doubt that here is another instance of the lower formation rising into the horizon of- the 

 upper. This is shown by Fig. 19, ante p. 251. 



Six miles to the west of this, on the shores of the Little Green Lake, the same 

 peculiarity is again manifested. At the southeast angle of the lake, a low arch is par- 

 tially exposed, while on the north shore a more decisive instance occurs. A precipitous 

 bluff, crowned with Trenton strata, skirts the lake on that side. At the west end of this 

 bluff, there are fifty-four feet of St. Peters sandstone between the Trenton layers and the 

 water's edge, and how much is concealed beneath is unknown. But within eighty rods 

 to the east, the Lower Magnesian strata rise above the water's edge, and approach 

 within eighteen feet of the Trenton above, if, indeed, they do not come into actual con- 

 tact, as the nature of the slope seemed to indicate, but which could not be observed on 

 account of the talus covering the side of the bluff. In the opposite direction, within a 

 half mile, the Lower Magnesian strata may be found arching upwards to elevations of 

 thirty and forty feet, or more, above the lake level. 



About half a mile to the northwest, a valley reveals the arcuate nature of the strata 



most clearly. On entering the gorge below, the layers are found to dip southward at 



an angle of 20 and upwards, but as the crest is mounted, the inclination becomes lesd 



and less until they are lost beneath the soil, within twenty feet of the Trenton horizon. 



Wis. SUR. 18 



