80 • GEOLOGICAL SURVEY OP WISCONSIN. 



rielderberg is above the Salina and below tbe Oriskany. Of course, 

 its stratigraphical relations vary in localities. The normal underlying 

 formations will be wanting where, during one or more preceding 

 epochs, emergence of the land had taken place and, consequently, the 

 ancient ocean, having receded, was not there busy with its work of 

 rock-making. 



For the same reason, in many localities, the normally overlying 

 series are entirely wanting. The Lower Helderberg, like the rocks of 

 any other period, are entirely wanting, where the dry land had ap- 

 peared before that particular epoch. Over a large area of Wisconsin, 

 for example, there are no rocks above the Arch^an, for the simple 

 reason that this area has been an emerged portion of the continent 

 since the primeval ocean first deposited the Laurentian and Huronian 

 formations. ISTowhere in the state do we find rocks of the Mamma- 

 lian, Eeptilian, or Carboniferous ages, because during all these long 

 divisions of geological time, "Wisconsin has been dry land. In other 

 places on the globe, the seas have continued their labor of rock-making, 

 but here the continent was finished long ago. In places portions of 

 the continent have been upheaved during one or more periods, and 

 then for a season submerged again by faster or slower subsidence. 

 During the period of emergence, rock-making has ceased ; with re- 

 submergence rock-making has gone on again. Thus epochs are want- 

 ing here and there, and the geologist has dynamical problems to solve 

 more diflicult than problems of lithology. 



The Lower Helderberg epoch takes its name from the Helderberg 

 mountains in the state of jSTew York, where the formation is com- 

 plete. Beginning from below, its subdivisions are: (1) The Tentacu- 

 lite or Water-lime group; (2) The Pen tamer us limestone; (3) The 

 Catskill or Delthyris shaly limestone; (4) The Encrinal limestone, 

 and (5) The Upper Pentamerus limestone. 



In this connection, it is necessary to consider more particularly the 

 lowest, or Water-lime division. In fact, the different subdivisions ob- 

 served in the Helderberg mountains, scarcely appear outside of New 

 York state. All of them but the Water-lime group disappear, even in 

 jSTew York, westward of Ontario county. • "This group," says Mr. 

 Vanuxem, in the New York state survey, " takes its name from its 

 earthy drab colored limestone, from which all the water-lime in the 

 district south of the Erie canal, with one exception, is manufactured. 

 It consists generally of dark blue limestone, and usually of two layers 

 of drab or water-lime stone; the two always separated by an inter- 

 vening mass of blue. The group is well defined, and is readily recog- 

 nized in this state and in Pennsylvania, by its mineral nature, its fos- 



