304 GEOLOGY OF EASTERN WISCONSIN. 



a detour to the eastward in range 31, and gives rise to Potato and Place's Rapids, where 

 the river crosses it, the former due apparently to the more resisting Lower Buff beds and 

 the latter to the Upper. 



The second series of rapids encountered in ascending the Menomonee river are attrib- 

 utable to a similar cause. It is much to be regretted that at this extremity of our dis- 

 trict, two hundred miles from the point where our study of the formation began, there is 

 not an equally extensive and fortunate exposure of its several members, that compari- 

 sons might be made which would exhibit the changes it has undergone in thickness, 

 hthologioal character and organic contents. Instead of this we have only a few feet 

 poorly exposed in the banks of the Menomonee river. A portion of the rock at the 

 rapids is a deep blue, heavy, crystalline Hmestone, weathering smooth and breaking into 

 rectangular blocks, while other portions are quite irregular in texture, being composed 

 of combined earthy, crystaUine and shaly material, with partings of the latter material. 

 The bedding is thin and the layers for the most part uneven. On the whole, while not 

 differing essentially from the general characters of the formation as seen elsewhere, it 

 presents an exceptional aspect in harmony with the sug-gestion already made, that this 

 formation in common with the accompanying ones below and above has changed, in a 

 subordinate degree, its peouhaiities. The following species indicate the character of 

 the fauna: A new species of Cruziana, Buthotrephis succulens, undetermined J'kcot'c^s, 

 Chwtetes lycoperdon, Monticulipora aUied to M. frondosa, Crinoidea ( Cyathocrinus? ) , 

 columns of Schizocrinus nodosus, a new species of Stictopora, Ptilodictya recta ? Orthis 

 testudinaria, 0. tricennria, and an undetermined species, Streptorhi/vchus filitextiim, S. 

 planocomvx uDi , Stri/phomena incrassata, Bhynchonella, Zygospira recurvirostra, Penta- 

 merus hemiplicatus, and TrUobitic remains {Asaphus).^ 



Industrial Considerations. This rock is extensively quarried for 

 the purposes of common masonry. At the great majority of places 

 the quarries are only superficial and the layers thin, and associated 

 with much chipstone. As greater depths are reached a better class 

 of building stone is usually found, because the rock has been less sub- 

 ject to surface action. It is to be observed, however, that with the 

 same amount of exposure the layers in the interior of a hill, which ap- 

 pear firm and solid, would become split and broken, like those that 

 outcrop. The change that is seen in tracing a layer back inio the 

 hill is brought about by the atmosphere, frost, percolating water, and 

 similar agencies, and is not due to the original nature of the rock. 

 This fact affords a means of judging of the endurance of the rock, 

 and, applied to most of the beds of this formation, shows that their 

 power of resisting the elements is limited. This is especially true of 

 the Blue limestone, which is inferior to the Buff", and which is to be 

 avoided as far as circumstances will permit. It is a matter of expe- 

 rience that two quarries may be opened with what appears to the 

 proprietors an equally good prospect, one of which will soon reach 

 regular, even courses, with little waste material, while the other only 

 develops thin layers with much shale and chipstone. Such would be 



■ Compare list from the same locality in the Michigan Report, Paleozoic Rocks 1872 

 p. 62. 



