308 Scientific Intelligence. 



an unconformability in Wisconsin is certainly a fact, established 

 not by one or two instances, but by man v. 'The ex:.. 



J often to he seen, the almost loose 

 sand of the Potsdam, with numerous fossils, as also fragments de- 

 rived from the older rocks, lying upon and wedged in between 



i ledges of Huronian quartzite, schist, or other rock. 

 Exactly similar unconformability is to be seen at the Dalles of the 

 bt. Croix River between the Potsdam and Copper 3< 



i beds of the former, tilled with shells of Li 

 lying directly upon the columnar melaphyre (?) of the latter serial, 

 the two series being exposed. Tin- en *tallin< 

 rocks of VV isconsin include unquestionably two distinct terranes, 

 the one lying unconformably upon the other, as is 

 shown at Penokee Gap, on Bad river, in the Lake Superior country. 

 Here a white siliceous marble of the Huronian, overlaid by hun- 

 dreds of feet of distinctly bedded slaty rocks, and dipping north- 

 ward, is to be seen within twenty feet of large ledges of dark col- 

 ored amphibolic gneiss, whose bedding planes dip southward and 

 $a mu direction diagonally across that of the more northern 

 beds. I here are no doubt instances where the two series are 

 difficult to sepsmit. . -i, ,i ; ,r rocks occuring in both groups, but the 

 existence of the two is incontestable, and their 



with the unaltered Potsdam equally so. The facts pn 

 tar with regard to the older rock series of Wisconsin may be 

 briefly summarized as follows: the oldest (I) are gneisses and 

 ■ otbei rocks; (base are overlaid unconformably by 

 (11) a series of quartzites, schists, diorites, etc., with some gneiss 

 • ; these in turn are ov« unconform- 



ably but this is not certainly proven-by (III) the Copper series, 

 which includes greenstones and melaphyres, and also great thick- 

 ified sandstone, melaphyres, amygdal 



these finally 



i.rmably covered by (TV) a series of unaltered horizo it:il 



nv of which are closely 



allied to those of the Potsdam sandstone of New York, and all of 



wtucb have a marked Primordial aspect. I and II are referred to 



the Laurentian and Huronian systems of Canada, because they 



to one another and to the Copper series 



However this may be, it will be seen that 



Wisconsin crystalline rocks within the 



. ould have to stretch that term so as to 



entirely distinct terranes, each overlying its prede- 



that these systems do. However this may be, it will be seen thai 



in order to i ■ , \, .,, \\- ... ,_;,, ,.. _ |i;| (ii ^ % i th inthe 



fr. Bradley would have to stretch that 1 



«■ * ----- — "v .».■! many thousand feet in thickness, U~ 

 SiStoi i * three in its tuni ov erlaid unconformably by hori- 

 zontal sandstone with Primordial fossils. As to any of the V\ i- 



the Primordial and neuvr <tr:,- ..,, such an 



nypothesis is certainly untenable for a moment Such 



and in all probability do occur in the Appalachians, but there 



