544 T. H. Holland — Rock-iceathering and Scrpentimzafion. 



quartz chiefly out of its felspars." ^ Scrope, even as far back as 

 1825, suggested that these secondary minerals in trap rocks are the 

 results of vapours accompanying volcanic eruptions, though he 

 admitted that additional material might subsequently be obtained 

 by the infiltration of solutions from overlying rocks, especially 

 "calcareous strata."^ In 1897 Sir A. Geikie pointed out that 

 though it is a common belief that the filling in of the steam cavities- 

 has taken place long subsequent to the volcanic period by the slow 

 percolation of meteoric water through the rock, he believed that 

 at least in some cases, if not all, the conversion of the vesicular 

 lavas into amygdaloids was effected during the volcanic period, the 

 amygdales themselves sharing in the general metamorphism induced 

 by later eruptions." 



Although different opinions are recorded concerning the origin of 

 certain of these secondary minerals, there is a fair agreement in 

 literature with regard to the ])ossible origin of secondary chlorite, 

 biotite, epidote, magnetite, and the amygdaloidal bodies in basalts 

 by the action of subterranean vapours, both during and subsequent 

 to the consolidation of the rocks in which they occur. Although, 

 moreover, more than one mode of origin has been granted for 

 certain of these minerals, I cannot subscribe to Professor Merrill's 

 verdict that " geologists and petrologists as a rule have been ex- 

 tremely careless in their use of such terms as alteration, decomposition, 

 and weathering." Eoth gave a wider meaning to weathering than 

 most, but before, during, and since his time many of the minerals 

 regarded by him as products of weathering have been referred 

 to deep-seated agencies. Kaolin and, with evident misgivings,- 

 serpentine have, however, until recently been generally looked 

 upon as the work of meteoric waters. After what has been written 

 above and published in other papers, it would be difficult to prove 

 that I entertain any predetermined bias against the action of deep- 

 seated agencies. On the contrary, knowing what has been done in 

 connection with epidote, chlorite, and the other secondary hydrous- 

 minerals just referred to, the first step to take, after abandoning th© 

 weathering theory, would most naturally be an examination of the 

 possibility of serpentinization by deep-seated agencies. 



The very facts, however, which indicate in India the insufficiency of 

 weathering to account for serpentine masses, point to quite a difierent 

 conclusion ; and until these facts have been shown to be purely 

 local and exceptional, or until they are proved to be necessary 

 accompaniments of some more far-reaching cause, the submarine 

 theory remains as the first and simplest inductive inference. Briefly 

 the facts are these : — At different points in the old crystalline land 

 area in the Madras Presidency, Mysore, and Coorg, we know of 

 more than a dozen occurrences of peridotites, chiefly dunites, but no6 

 a single mass of serpentine. In the Andaman Islands, Burma, 

 Kashmir, Baluchistan, and near the North- West frontier — areas whicb 



^ Amer. Jouru. Sci., ser. in, vol. xx (1880), pp. 331-2. 



2 " Cousiderations on Volcauoes," 1825, pp. 126-7. 



3 "Ancient Volcanoes of Great Britain," 1897, vol. i, pp. 16, 17 ; vol. ii, p. 18^. 



