466 HISTORICAL GEOLOGY. 



significance is tlie igneous origin of a large part of the formation. Sheets 

 of basic igneous rocks, partly amygdaloids, with others of felsyte, porphyry, 

 and granite, are interstratitied with the sandstones and conglomerates, and 

 the latter are largely made of water-worn detritus of like igneous origin. 

 The beds are wholly unmetamorphic to the bottom, and hence there is 

 nothing in them to prove that the formation is Archaean. At the same 

 time, no fossils have beeii found to prove it Cambrian. Still, inasmuch 

 as it overlies unconformably the upturned Huronian, it must be of sub- 

 sequent origin ; and as no Cambrian rocks occur in Wisconsin older than the 

 Middle Cambrian, it is reasonable to suppose that it may represent the Lower 

 Cambrian. The absence of fossils may be owing to the region's having been 

 under fresh water, or to the igneous action. The copper veins of the Kewee- 

 naw region have been discussed on page 341, under the head of Veins. 



It is important to note, however, that the igneous effusions which accom- 

 panied the deposition of beds below the Lower Cambrian in southeastern 

 Pennsylvania and the adjoining borders of Maryland, are similar, as Williams 

 remarks, to the rocks of the Keweenaw series not only in kinds, but also in 

 the presence of much metallic copper. Waleott and Williams conclude that 

 the eruptions in the two areas were simultaneous and alike pre-Cambrian. 



Bearing of the facts connected imth the distribution of the Cambrian on 

 questions as to the upturning preceding the era. — From the facts observed 

 in connection with the distribution of the Cambrian over the Archaean of 

 northern New York and Canada and in Archaean troughs to the eastward, it 

 appears to follow that the mountain ranges in eastern America that were 

 made at the close of the Archaean, and that stand as the time-boundary 

 between the Archaean and Paleozoic, include the Adirondacks, the Appa- 

 lachian protaxis, and other more eastern ridges ; and that these mountains 

 consist, in part, if not largely, of rocks that were laid down as sediments 

 during the long Huronian era, though now crystalline or metamorphic and 

 in part massive crystalline. The disturbances closing Archaean time do not 

 appear to have extended their effects alike over the whole surface of the 

 continent, but to have produced their chief uplifts along the mountain 

 borders ; that is, in those regions in which the most extensive mountain- 

 making occurred in later time. Over the Continental Interior, the Huronian 

 sediments were thinner, the upturnings at the epoch of disturbance less 

 prominent, and the metamorphism feebler, where not wholly wanting. 



Waleott has classified the areas of geogi-aphic distribution of the surface outcrops 

 of the Cambrian strata as follows {Bull. 81, TJ. S. G. 5., page 358) : — 



A. Atlantic or Eastei'n Border Province : a, Eastern or Nova Scotia Basin ; &, South- 

 eastern Newfoundland, Eastern New Brunswick and Massachusetts Basin ; c, Interior 

 Deposits of Gaspe, Quebec, Maine, New Hampshire, Vermont, Massachusetts. 



B. Af)palachian or Interior Eastern Border Province. 



C. Rocky Mountain or Western Border Province. 



D. Interior Continental Province : D i, Central Interior, or Upper Mississippi and 

 Missouri ; D "', Eastern Interior, or Adirondack of New York and Canada ; D 3, Western. 

 Interior, or Dakota, Wyoming, etc. ; D *, Southwestern Interior, or Arizona and Texas. 



