T. H. Holland — Roch-iceathering and Serpentinization. 545 



liave been covered by Tertiary marine sediments — we know of about 

 the same number of peridotite occurrences, which are all highly 

 serpentinized. Fresh olivine is as scarce in the areas which have 

 been submerged as serpentine is in the old crystalline block of 

 Peninsular India, which has suffered uninterrupted subaerial denu- 

 dation since at least Lower Pal£eozoic times. In the latter area it is 

 not merely the dunites which have escaped hydration ; the olivines 

 of the basic dyke-rocks are equally fresh. If serpentinization is due, 

 as Professor Merrill suggests, to waters or vapours coming from 

 considerable depths, it is difficult to see why these rocks, erupted at 

 different times and in well- separated localities in Peninsular India, 

 should universally escape, whilst in the other areas mentioned, also 

 widely separated by great distances, serpentinization should be so 

 constant. With evidences of the action of deep-seated vapours in 

 other ways in Peninsular India, the value of this point becomes 

 accentuated. Besides olivine, other minerals, notably nepheline, are 

 remarkably free of hydration iti the Madras Presidency. 



It was pointed out at Bristol that whilst fresh peridotites occur in 

 a moist warm climate exposed to heavy rainfall, serpentines are 

 found in the dry deserts of Baluchistan, and Professor Merrill has 

 now produced similar evidence from America to show that the 

 distribution of serpentine and of unaltered olivine-rock does not 

 coincide with any general difference of climate. On the other hand, 

 the areas containing serpentine have been submerged below the sea, 

 whilst those in which fresh peridotites occur, so far as we know, 

 never have been. The first inference is obvious, and the next duty 

 is to discover if these circumstances in India are merely local 

 accidents or in general agreement with the evidence obtained in 

 other parts of the world. For this we must await the testimony 

 of geologists who possess the necessary local knowledge. 



By his reference to the fresh condition of the olivine in the 

 Corundum areas of western North Carolina, Professor Merrill cites 

 a case which appears to be in agreement with our observations in 

 India. The crystalline belt which runs N.E.-S.W. through North 

 Cai'oliua is one of the few persistent sturdy old blocks of crystalline 

 rocks which have been unaffected by late earth movements.^ It 

 apparently formed the south-eastern boundary of the old Palaeozoic 

 seas, and suffered a marine trespass only on its eastern borders 

 during the Mesozoic and Tertiary times.^ The distribution of the 

 marine sediments and the principal directions of folding indicate 

 that this crystalline ' Scholle,' to quote Suess' terminology, presents 

 to the Appalachians a relation similar to that holding between our 

 Peninsular ' Vorland ' and the Himalayas. Here we have the 

 negative side of the argument — in an area not known to be 



1 This belt has been the only serious rival with which Peninsular India has had to 

 compete in the mica market, and the preservation of large sheets of delicate muscovite 

 in coarse-grained pegmatite is generally a safe index of geological stability and 

 quiescence. 



2 See Dana's " Manual of Geology," 4th ed. (1895), pp. 412, 443, 536, 633, 735, 

 813, and 881. 



DECADE IV. — VOL. VI. — ^NO. XII. .35 



