226 Eevieus — Br. J. Petersen on Cheviot Bocks. 



islands which are igneous — except St. Paul's Eocks, about which 

 there exists some doubt ^ — have been classified as oceanic. 



In Jules Marcou's Geological Map of the World the island appears 

 to be about the size of Cyprus. The scenery, according to the 

 Expedition, in spite of its desolateness, possesses a beautiful Alpine 

 character, the tranquillity of which was only broken by the constant 

 thunder of avalanches. The mountains are from 2000 to 3000 metres 

 high, and in places they plunge abruptly into the sea. Now, as we 

 do not find high mountains composed of sedimentary strata, excepting 

 the strata be of vast extent and thickness, it is reasonable to infer that 

 these sedimentary rocks are not confined to the island, but extend 

 far under the ocean bottom. It is also a self-evident truth, that 

 these sediments must have been derived from a pre-existing land of 

 great area, probably continental. The curious in such matters may 

 speculate whether it lay to the north, south, east or west. x\s there 

 is at present absolutely no data to go by, each inquirer may solve it 

 in a way to suit his own views best, which is comforting. 



If the foregoing reasoning be admitted as valid, it not only re- 

 claims a very large area of land from the ocean, but strikes a vital 

 blow at the " permanency " hypothesis, as built up on the supposed 

 non-sedimentary character of oceanic islands. 



I have in former Numbei's of this Magazine given my views on 

 the untenability of the reasoning in favour of Permanence of Oceans 

 and Continents,^ and a somewhat similar class of arguments to mine 

 and to the same end have since been advanced by Mr. W. 0. Crosby.^ 



It would be interesting to have soundings round the island, to 

 see if the mountain range extends under the sea as a submarine 

 ridge. 



It may be added, that no land mammals were found on the island. 

 Their absence has been held by Mr. Wallace to prove that such 

 islands were ever islands. It has always appeared to me that this 

 generalization — hinging as it does on negative evidence — has been 

 elevated into too much importance. 



ia:E"V"i:E"ws. 



Dr. J. Petersen on Some Cheviot Eocks. 



MiKROSKOPISCHE UND ChEMISCHE UnTERSUCHUNGEN AM EnSTATIT- 



PORPHYRiT aus DEN CHEVIOT HiLLs. Inaugural Dissertation von 

 Johannes Petersen. (Kiel, 1884.) 



THE specimens which Dr. Trechmann collected during my second 

 visit to the Cheviot district were forwarded by him to Prof. 

 Eosenbusch, and form the material on which the observations 

 recorded in this communication are based. Coming as it does from 

 one of the first petrological laboratories in the world, we are not 



1 Eeporfc on the Petrology of St. Paul's Eocks, by M. Renard (Challeng-er Reports). 

 Recifs de St. Paul, par M. Renard, Annales de la Societe beige de Microscopie. 



'^ Oceans and Continents, Geol. Mag. Sept. 1880, p. 385, and Oceanic Islands, 

 Feb. 1881, p. 75. 



2 Origin of Continents, Geol. Mag. Decade II. Vol. X. June, 1883. 



