Correspondence — Rev. ' 0. FUher. 525 



MR. FISHEE'S REJOINDER TO MR. T. MELLARD READE. 



Sir, — In my letter, at p. 431, on "The Permanence of Ocean 

 Basins," I said that South Georgia might fairly be excluded from 

 the category of Oceanic Islands, as having been perhaps formerly 

 joined to South America. The bearing of this upon the question 

 seems to me to be that, if it had not been formerly connected with 

 some still existing continent, it might be argued that it had be- 

 longed to a submerged one. But if it formed once part of one now- 

 existing, that conclusion would not be necessary. Moreover, it stands 

 a witness to the antiquity of South America, because of the length 

 of time which must have been occupied in the destruction of the 

 connecting land. 



Those who believe in the doctrine of permanence do not assert 

 that the continents have always had their present size or shapes, but 

 only that, on the whole, they have not changed places with the 

 oceans. 0. Fishek. 



Harlton, Cambridge, &th Oct. 



THE CLASSIFICATION OF THE JURASSIC SYSTEM. 



Sir, — The Geological Magazine for July contained a short paper 

 by Mr. Blanford on the Classification of Sedimentary Strata, with 

 a Table, which aimed at the simplification of our present strati- 

 graphical nomenclature. None of our geological systems stand more 

 in need of revision and simplification than the Jurassic, and I think 

 many will welcome the suggestion that this system should be 

 divided into three sections or stages, and three only, — an Upper, 

 Middle, and Lower, as Mr. Blanford proposes. 



An Oolitic system, as separate from the Lias, is quite unnecessary, 

 and it would be desirable that the term Oolite should be used only 

 as a lithological appellation for a particular kind of rock, though 

 there can be no objection to the retention of such compound names 

 as Inferior Oolite and Great Oolite for groups which are chiefly 

 composed of oolitic limestones. But let the name " Lower Oolites " 

 be banished from our text-books. I can recollect the time when it 

 was a trouble to remember that Inferior Oolite was not the same as 

 Lower Oolite, and I cannot but think that the abolition of this 

 possible source of confusion would be a benefit to young students of 

 geology. 



I feel confident that the divisions or stages of Upper, Middle, and 

 Lower Jurassic will be ultimately accepted, but I venture to differ 

 from Mr. Blanford in the manner of grouping the minor subdivisions 

 under these heads. 



The Lower Jurassic is of course synonymous with the Lias. The 

 Middle stage should, in my view, comprise the overlying beds up 

 to and no farther than the Cornbrash, and should certainly not 

 include the Oxford Clay. The Cornbrash is a well-marked and 

 nearly continuous horizon in England, and forms the natural 

 summit to a group which is essentially composed of oolitic lime- 

 stones. With the Oxford Clay, which includes the Kelloway rock 

 near its base, begins a series which is essentially argillaceous or 



