Frof. T. G. Bonney — Remarks on Serpentine. 411 



that botb in associated minerals and in chemical analyses the serpentines 

 and peridotites are closely related. Dr. Hunt, howevei', endeavours 

 to show that the bulk of the peridotites are of sedimentary origin. 

 Obviously the point is not settled by proving tbat olivine may occur 

 in a sedimentary rock. We have mica in mica-traps and in mica- 

 schist ; quartz in felstones and in the geodes of sedimentary rocks ; 

 augite in dolerite and sahlite in crystalline limestone ; hornblende in 

 many rocks both metamorphic and igneous, etc. What, however, 

 are the facts of the case ? Dr. Hunt asserts the presence of olivine 

 (but not, as it appears, the variety usually found in peridotites) in 

 certain limestones of Eastern Massachusetts. Olivine is also said 

 to occur in nodules in a talc-schist from the Urals, and in a 

 talc-schist from Mount Ida; of these I have not seen specimens, 

 but after reading the account in Science to which Dr. Hunt refers, 

 I do not feel certain that in the latter instance we may not have 

 a case of pseudo-schistose structure due to subsequent pressure, with 

 the production in the more crushed parts of a serpentinous or talcose 

 mineral. I may remark here that Dr. Hunt has forgotten to quote 

 another part of the same authority,^ where it is stated, " The serpen- 

 tine in the anterior part of the Troad has been derived from olivine- 

 enstatite rock of a truly eruptive character." 



Dr. Sterry Hunt's theory requires that serpentines should be all of 

 Archaean age. Whether I am right or not in my view of the Italian 

 serpentines, — and I must say that stratigraphically Dr. Hunt's view 

 appears to me most impi'obable, — I must ask him to consider the case 

 of the serpentine in Forfarshire, described long since by Sir Charles 

 Lyell. I am assured by one of our best English geologists and 

 petrologists that it indubitably forms a dyke in the Upper Old 

 Red Sandstone, and I can myself answer for the rock being a true 

 serpentine. 



He relies also upon some cases of olivine rocks occurring in 

 Norway. In all the accounts of these to wliich I have been able 

 to obtain access, the evidence of a transition from the admitted schist 

 to the peridotite appears to me defective. An apparently regular 

 interbedding with sedimentary rock does not suffice, or we should 

 have to assign a sedimentary origin to some Scotch basalts and 

 pitchstones. Nor is some indication of a foliated structure con- 

 clusive ; for that can be produced locally in an igneous rock when 

 it is subjected to a pressure in one direction, while the structure of 

 every olivine rock that I have seen in the field or examined with 

 the microscope (including some of the Norway peridotites) is that 

 of a rock of igneous origin. 



This then is really the state of the case. Olivine (one of the most 

 frequent constituents of meteorites) is an abundant mineral in rocks 

 which must be of igneous origin ; it is rare in those of sedimentary ; 

 many even of the cases alleged being so doubtful that we may 

 perhaps be able to write — extremely rare. The structure of tlie 

 olivine rocks, in those cases which are certainly intrusive, agrees with 

 that of other cases which are at present uncertain. Many serpentines, 

 1 Science, 1883, p. 255. 



