L90 A. C. LAWSON — RELATIONS OF Till-: A.RCHEAN OP CANADA. 



* * *. lis [micaschistes] y alternent avec des lit-- subordonnes de gneiss a grains 

 fins, d'ampbibolites, de chlorito schistes, de schistes micaces, et comprennent des 

 masses interstratifiees de diorites el de granulites, d'origine eruptive. Ccs roches 

 subordonnees for men t avec los micaschistes, dans lesquels elles sont injectees, de 

 longues bandes paralleles, * * *."* 



Newton's description of the geology of the Black Hills of Dakota i haves 

 little room for doubt hut that the rucks which he calls Archean correspond 

 to the upper Archean or Ontarian system of central Canada, and that his 

 irruptive granite, though not described as foliated, is the analogue of the 

 commonest phase of the Laurentian. The same relationship holds between 

 the two rock systems in both regions, and many of the Laurentian granites 

 are devoid of foliation. 



Geognostical Equivalents of the Archean. 



In assemblages of rocks of indeterminate or post-Archean age complexes 

 of gneissic irruptive rocks and older metamorphic strata of elastic or vol- 

 canic origin are now well known. These cannot be Bpokenofas the geolog- 

 ical equivalents of the Archean complex on account of their diverse age, but 

 may he referred to as Its geognostical equivalents, since their development 

 appears to depend upon universal sub-crustal conditions, which are to a large 

 extent independent of geological age. 



M<Mahoii,i in his studies of the great " central gneiss" formation of the 

 Himalaya mountains, has demonstrated clearly that the formation is not, as 

 was long Bupposed, the Archean basement upon which the Paleozoic sedi- 

 ments were deposited, hut is an irruptive mas- breaking up through the 

 Silurian and later rocks, altering them, holding detached fragments of their 

 strata, and being injected within the strata. Speaking of this formation, 

 which he ••all- gneissose granite, he cites the following evidences in proof ol 

 it.- irruptive- origin : 1. The granite has produced a certain amount of con- 

 tact metamorphism on tic rock.- touching it. 2. Tongue- and intrusive 

 veins have been sent from the granite into the adjoining rocks; in other 

 places the granite appears in Bheets between the he. Is of the sedimentary 

 rock.- ;it -nine distance from the junction of the latter with the main mass ol 

 the granite, and in -one cases these Bheets or dike- have cut through the 

 beds and passed from one horizon to another. 3. The main ma-- of the 

 granite appears at different geological horizons. § 1. The granite < tains 



Hull. Si i'-. I XIV, 18* 



y and Resouxcea "i the Black Bills <>i Dakota. By Benry Newton and 

 Walter I'. Jem 



rvej of I. ..i i:.. i: >k Vol. .Will, Pari I, 1884, p 108 ibid., Vol. XVIII, Pari 2, 1886, 



Oeol. Mag Dec ide III, \ ol. IV, 1887, p. 212. 



t does wl • tbe !<• tod al another against the Cout- 



liinR in i' on. 



