XIII. ] ORIGIN OF CRYSTALLINE ROCKS. 299 



mineral species were abundant in solution. The relation be- 

 tween these endogenous deposits and the great beds of orthoclase 

 and triclinic feldspar rocks is similar to that between veins of 

 calcite and of quartz and beds of marble and travertine, of 

 quartzite and hornstone. But while the conditions in which 

 these latter mineral species are deposited from solution are per- 

 petuated to our own time, those of the deposition of feldspars 

 and many other species, whether in veins or in beds, appear to 

 belong only to remote geological ages, and at best are represented 

 in more recent time only by the production of a few zeolitic 

 minerals. See in this connection the paper on Granites and 

 Granitic Vein-Stones, XL of the present volume, passim, but 

 especially 30, 31, and 49.] 



While, however, there is good reason to believe that solu- 

 tions of alkaline silicates or carbonates have been efficient 

 agents in the crystallization and molecular rearrangement of 

 ancient sediments, and have also played an important part in 

 that local alteration of sedimentary strata which is often ob- 

 served in the vicinity of intrusive rocks, it is clear to me that 

 the agency of these solutions is less universal than once sup- 

 posed by Daubree and myself, and will not account for the 

 formation of various silicated rocks belonging to the crystalline 

 schists, such as serpentine, hornblende, steatite, and chlorite. 

 When I commenced the study of these crystalline strata I was 

 led, in accordance with the almost universally received opinion 

 of geologists, to regard them as resulting from a subsequent 

 alteration of paleozoic sediments, which, according to different 

 authorities, were of Cambrian, Silurian, or Devonian age. 

 Thus in the Appalachian region, as we have already seen, they 

 have, on supposed stratigraphical evidence, been successively 

 placed at the base, at the summit, and in the middle of the 

 Champlain division of the New York system. A careful chem- 

 ical examination among the unaltered palaeozoic sediments, 

 which in Canada w r ere looked upon as the stratigraphical equiv- 

 alents of the bands of magnesian silicates in these crystalline 

 schists, showed me, however, no magnesian rocks, except cer- 

 tain silicious and ferruginous dolomites. From a consideration 



