T. S. Hunt—The Decay of Rocks. — 197 
§ 18. The existence, in the Laurentian series, of limestones, 
not less than that of iron-ores and of graphite, pointing to the 
existence of land and of vegetation during the deposition of the 
Laurentian, forces us to conclude to a process of sub-aérial decay 
of the more ancient gneisses in that far-off period. Such a pro- 
cess must have been continued in later times to give the mate- 
rials for the aluminiferous sediments of the newer eozoic 
examining with Dr. Credner a large collection of these, which 
Consist chiefly of types of various kinds of paces ee 
those of the Laurentian series as seen in North America an 
tu the Alps. These Saxon mica-schists, with their associated 
gneisses passing into granulites or leptynites, have all the char- 
acteristics of the Montalban or newer gneissic series of North 
America and of the Alps, to which I have elsewhere com red ; 
them in two communications” wherein are noticed the above- 
Mentioned conglomerates, which had been previously studied 
m-much detail by Sauer” in 1879. No one who. sees these 
accumulations of rounded masses of gneiss and other crystalline 
rocks entering into conglomerates at the various horizons above — os 
named, can fail to be struck with their close resemblance with = 
= Pe se 
5, Ceol. Magazine, Jan. 1882, p. 39, and Bull. Soc. Géol. de France, x, 26. 
Zeitschrift f. d. ges. Naturwiss, Band lii. 
