60 THE PENOKEE IRON BEARING SERIES. 



bands of varying cliemical constitution, (3) in the verging of one kind of rock into 

 another laterally, aiid (4) in kinds of rock not known to be produced by igneous 

 agencies. The whole series has been distorted, folded, and crumpled in a most intri- 

 cate manner, and the rocks, as the above names imply, are in a highly crystalliue 

 condition. It is manifest that the series was not so formed originally (pp. 64-60). 



Thickness. — The thickness to which these sediments accumulated was something 

 enormous. In their present crystalline state the current estimate of 30,00(1 feet is 

 probably not too great for the exposed portion, though the original Canadian 

 measurement on which it is based included beds now referred to the Huronian series. 

 IIow much may lie below is not known, since the base is not exposed. So great an 

 accunuilation could only have taken place on a subsiding bottom (p. 69). 



Distortion of the beds. — The long period of Laurentiau subsidence and sedi- 

 mentation at length drew to a close and the accumulated material underwent a most 

 extratn-dinary transformation. The sands and clays lay originally in essentially hori- 

 zontal beds, but at present we neither lind iiorizontal l)eds nor sands nor clays. The 

 strata are crumpled and folded in the most intricate manner. Not only have the 

 great series of beds been arched and compactly folded upon themselves, but even 

 the thin laminations have been contorted and crumpled in the most remarkable man- 

 ner. The axes of the folds in the region of northern Wisconsin run mainly north 

 east and southwest, varying several points in either direction. On the soutliwcstern 

 margin, however, there is a tendency to a more westerly and northwesterly trend, 

 somewhat parallel to that margin of the area (pp. 72-73). 



Attending metumorphism. — The crystallization of the material is strikingly in 

 harmony with this hypothesis of its heated condition. The sediments, while still in 

 their horizontal position, doubtless became solidified into somewhat firm rock (1) by 

 their own weight, (2) by their tendency to cohere, and (3) by the agency of cementing 

 infiltrations. But there is no reason to suppose that this induced any notable degree 

 of chemical or crystalline change. But in their present metamorphosed condition, 

 instead of compacted sand and clay, we find thoroughly crystallized rock, in the form 

 of granites, gneisses, syenites, hornblendic, chloritic, and micaceous schists. These 

 show that a profound chemical change has taken place, wherein the matter assumed 

 new combinations. At the same time, compounds of like kinds collected together, 

 under the control of crystalline forces, and assumed the form of definitely crystallized 

 minerals. Sediments that may originally have been a sandy clay, composed of silica, 

 alumina, and potash, mainly, formed granites, gneisses, or mica-schists. The potash, 

 alumina and quartz united in part to form orthoclase feldspar, or, in dift'ereut propor- 

 tions, together with magnesia, to form a mica, while the excess of silica took the form 

 of crystalline quartz. Tlie minor incidental constituents of the sediments entered into 

 these minerals as rei»lacement elements, or as impurities, or formed distinct accessory 

 minerals. When, as in some cases was true, there was a larger proportion of the 



