558 PROCEEDINGS OF NEW YORK MEETING. 



the Rainy lake district ih of Lake Superior (Part F, Ann. Rept. Geol. Canada, 



[887 Dr. A. Winchell has referred to similarcases in the paper just read. 



The characteristic featu usually the following: 1. The area was originally 



highest in the center, though now it lias reached the Benile topographic Btage. '2. 

 There is a concentric arrangement of the rocks and minerals. Thus, in a small ar«a 

 in Hanover, New Hampshire, the interior core displays porphyritic crystals of ortho- 

 clase, while the main mass consists of a rather coarse protogenic gneiss. The outer 

 band, not more than ](») or l'00 feet thick, has a superabundance of chlorite with 



hiotite, hut must not I nfounded with what have been called Huronian schists in 



the neighborhood. Thi- area is perhaps ten miles long and four miles wide. 3. T 

 foliated planes possess the anticlinal quaquaversal arrangement. Subsequent action 

 baa folded these planes just as if they indicated an original sedimentation. 



The significance of these facts depends upon the interpretation i;iven to the foliation. 

 [f these represent lines of sedimentary accumulation, then the are:,- constitute the 

 very oldest known stratified deposits. As they are anticlinal in form they furnish no 

 evidence of a basin structure ; or if the older foundation exists it lias never been ob- 

 served. There seems to be no evidence of sedimentation in these basal layers — all the 

 supposed conglomerates of the Archean being situated in the upper part of the group. 

 The facta are at variance with a popular notion of an indefinite series of systems, each 

 one formed from another concealed from view. The areas described arc the oldest 

 known, or fundamental rock-. 



If the other, or igneous view of origin be accepted, essentially the same view of 

 age must be entertained, for the -pace- between these primitive areas arc composed 

 of later Archean or Paleozoic rocks, and there are no apophyses or veins extending 

 into the newer series. Where these arc observed, as is claimed by Dr. Lawson, there 

 is reason to believe in their later igneous development. In tie icamined, every 



part of the concentric structure i- apparently of the same age, the zonal condition re- 

 sulting from freedom of motion in a plastic mas- so that there may be a segregation 



of like mineral constituents into separate hands. 



The origin of the igneous masses may he compared to the building up of oceanic 

 islands of the presenl day from volcanic ejection. I have elsewhere suggested ■ that 

 in New Hampshire the rounded areas of the oldest rocks are numerous enougb to have 

 constituted an archipelago which may have been the beginning of the Archean con- 

 tinent in New England. 



The area- of granite, syenite, and porphyry in the White mountains correspond 

 topographically with tbe supposed original Laurentian area-, hut they lack the planes 

 of foliation. Hence they cannot have been subjected to the influences which have 

 been brought to hear upon the former. Granting pondence between the two, 

 the one may represent youth and the other old age of igi us overflows. 



Professor 6. II. Williams: It is interesting to Bee bow the -a me facts may suggest 

 to different mind-, different interpretation- After what I have Been in Norway and 

 elsewhere an explanation occurs to me exactly opposite to the one which Professor 

 Hitchcock ha- Led. The center of the mass is, I think, the youngest, while the 



other layers are to be accounted for as having 1 n approximately horizontal Btrata, 



pushed up by a molten mass rising from below after (he other material was formed. 

 This eruptive rock has altered the Btrata progressively from the center. 



tddre lloa E, Proc. A. A. A. 8., vol. XXXII, 188.1. 



