404 THE CANADIAN NATURALIST. [Dec. 



repaired, if we may so speak, by an effusion of njineral matter 

 from the walls, and thus are generated geodes, irregular masses 

 and many veins. That the process imagined by Volger may in 

 some cases intervene, and may act subsequently to the one just 

 imagined, is highly probable, though we are disposed to assign it 

 but a secondary place in the production of vein-fisures. It offers 

 however the most plausible explanation of the distortion of the 

 thin-bedded strata already noticed in connection with some of the 

 concretionary granitic veins of Maine, which seem, by a process of 

 "Towth. to have bent outward the adjacent beds. The vertical 

 transverse veins are, in many cases at least, unsymmetrical, as if 

 they had grown from one side, while the distortion of the beds, 

 sometimes attended by irregular concretions in the banded vein- 

 stone, appears at the opposite wall. The notion that the vein- 

 fissures opened as crystallization advanced, has been defended by 

 Griiner. 



§ 28. It is not here the place to discuss how far the greater 

 and deeper fissures of the earth are dependent upon the contraction 

 of sediments, as just explained, or upon the wider spread move- 

 ments of the earth's crust, though even of these it may be said that 

 they are more or less directly the results of a process of contraction. 

 It should however be noted that while some fissures of this kind 

 are filled with dykes of erupted rocks (§ 2(3), others hold concre. 

 tionary veins, which are to be distinguished from the class of 

 veins just described, inasmuch as the openings in which they were 

 deposited evidently communicated with the surface of the earth. 

 Examples of these are seen in the lead and zinc-bearing veins with 

 calcite amd barytine, which traverse vertically the carboniferous 

 limestone in England, and enclose in their central portions material 

 of liassic age, abounding in the remains of a marine and a fresh, 

 water fauna, which show these veins to have been deposited in 

 fissures communicating with the surface-waters of the liassic period. 

 For a description of these veins by Mr. Charles Moore, see the 

 Report of the British Association, for 1869, and Amer. Jour, of 

 Science II, 1, 365. Similar evidence is afforded by the existence 

 of rounded pebbles imbedded in veins, as observed in Bohemia, 

 and also in Cornwall, where numerous pebbles both of slate and 

 quartz were found at a depth of six hundred feet in a lode, cemented 

 by tinstone and sulphuret of copper. (Lyell, Student's Elements 

 of Geology, p. 593. Not less instructive in this connection are 

 the observations of Mr. J. A. Phillips, on the silicious veinstones 



