508 THE AZOIC SYSTEM AND ITS SUBDIVISIONS. 



four groups, a classification which, as he states, Professor Zirkel's " mi- 

 croscopic examinations every way confirm " ; but, in point of fact, the 

 latter divides them into two classes, the older eruptive granites contain- 

 ing no titanite, and the younger eruptive or Jurassic granites which 

 are characterized by the presence of that mineral. (VI., pp. 58, 59.) 

 The Wahsatch granite is regarded as the most characteristic type of 

 the younger or Jurassic granites bearing titanite. (VI., pp. 50-52.) 

 We have been unable to find in the writings of Messrs. King, Emmons, 

 and Hague any statement why their ideas of the age of these granites 

 underwent so radical a change after 1876, — any reference to new evi- 

 dence discovered, or to the views previously held, — or how, in the light 

 of what Professor Zirkel says in the chapter upon granite, he can be 

 quoted as then sustaining Mr. King's views as published in 1878. 



If Mr. King's ideas regarding the origin of the supposed Archaean are 

 correct, thus far he has not been able to show that the rocks with which 

 the Archcean is in contact are older than the Quebec group. In fact, 

 he and his assistants have failed to bring forward any proof of value in 

 support of their position. Rocks found in contact with others show 

 by their relations, as a general rule, whether they (1.) were deposited 

 against them as a sea-shore cliff; (2.) have been pressed against and 

 through them as a solid mass; (3.) were chemically deposited in con- 

 tact ; (4.) came as intrusions, overflows, or in any other way. Each oc- 

 currence has its own individual characters. These characters, in the 

 study of cases like the preceding, should be known from the examina- 

 tion of rocks whose origin and relations are known. We fail to find 

 any evidence in their publications that Mr. King and his assistants 

 looked for that proof which, if their views are correct, should exist in 

 overwhelming abundance. 



Where sedimentary rocks of Potsdam age have been deposited in 

 contact with the Azoic rocks of Lake Superior, they show by the en- 

 closed fragments that they were derived from the latter ; they show, on 

 examination of the contacts, that the Potsdam was deposited against a 

 water-worn cliff; no sign of mechanical, eruptive, or any other force, 

 except the impact of water, is to be observed. Had there been other 

 forces acting to any amount along the contacts their effects would have 

 been visible, and their history could be made out to a greater or less 

 extent. So in the case of the Wahsatch Mountains, if the Pal<Teozoic 

 rocks were deposited against such cliffs as Mr. King imagines to have 

 existed, the evidence to prove this should have been sought for. Abun- 

 dant debris from the cliffs ought to have been found in the Palaeozoic 



