DECOMPOSITION OF ROCK BY CORROSIVE ACTION 



53 



defined border of the decay on the east, at once suggest its possible 

 connection in some way with this chemical action. This might be 

 referred to an attack of the schist by the magma tic vapors, "the 

 post- volcanic gas exhalations" of Weinschenk, accompanying the 

 eruption of a dike of acid constitution, but for the entire absence 

 of such effect in the vicinity of the tourmaline-bearing granite 

 dikes which abound throughout this region. Taking all the facts 

 here observed, we conclude that at this locality we find proofs, in 

 the deep erosion, solution, and leaching, of the long-continued 

 action of humus acids from peat-water, resulting in products which 

 correspond to the 

 "Grauerde" of Ger- 

 many, studied by 

 Ramann, Wiist, 

 Selle, Stremme, etc. 1 

 It seems probable 

 that this deep local 

 decay of both gneis- 

 sic schists and the 

 inclosed pegmatite 

 records the continu- 

 ous corrosion of an 

 ancient pre-glacial 

 peat-bog. The east- 

 ern border of the bog 

 appears to be marked 



by the sharply defined eastern limit of this decayed tract. The 

 wall of impervious pegmatite may perhaps have formed a dam to 

 confine the corrosive liquids, as in a vat, along this edge of the 

 ancient bog; in such case the limit of corrosion would naturally He 

 parallel to the line of the dam. 



With the prevalent tendency to attribute the formation of the 

 original layer of laterite over the northern part of our continent 

 mainly or exclusively to weathering by meteoric agencies, there 

 seems to have been little recognition of the view above suggested 

 in explanation of the local instances of deeper decomposition of 



J H. Rosier, Zts.f. prkt. GeoL, XVI (1908), 251-54. 



Fig. 7. — Showing how a bowlder was forced into one 

 of the transported slabs. 



