Correspondence — R, Mallet. — G. H. Kinahan. 189 



N.W. of England it is a strikingly original formation, as proved by 

 the fi'eshness of the numerous and generally parallel striae on the 

 included stones. It is, however, confined to low levels. 



D. Mackintosh. 



FUETHER REMAEKS ON VULCANICITY. 



Sir, — The statement of your footnote at p. 127 of my Eeply to 

 Mr. Scrope (Geol. Mag. for March, 1874), in which you say that 

 "Mr. Mallet in this and other passages certainly misapprehends 

 Mr. Scrope," does not seem to me justified by the facts, and I beg 

 of you to permit me to explain why. 



The objections made by me to the supposition of a thin crust and 

 a great liquid nucleus are alike applied by me to the hypothesis of 

 Hopkins, of a thin crust covering his subterranean liquid lava lakes. 

 I have throughout my reply linked these together. Whether, there- 

 fore, Mr. Scrope now continues to adhere to the former notion, as I 

 am warranted in taking from the tenor of almost all his writings, — ■ 

 or whether, as in the papers in the Geol. Mag. Vols. V. and YI., to 

 which you direct attention, he more recently is disposed to abandon 

 the moribund thin crust and liquid nucleus theory, and to fall 

 back upon the thin crust and fiery lakes of Hopkins (for the views 

 in the papers above referred to seem to me neither more nor less 

 than that), — I have not, as I believe, — certainly not consciously, — • 

 misapprehended Mr. Scrope. The difficulties of Hopkins' notion, as 

 adopted by Mr. Scrope, are just as great as those of the older one of 

 thin crust and liquid nucleus, with this additional disadvantage, — ■ 

 that whereas the latter is an assumption that may stand alone, the 

 former (Hopkins' or Mr. Scrope's) is an hypothesis as arbitrary, and 

 which cannot be admitted at all without admitting another hjqjo- 

 thesis previousl}'-, upon which it must depend. 



Kith March, 1874. EoBEET MaLLET. 



ORIGIN OF THE FLEET. 

 SiK, — I can assure Col. Greenwood that I have read his valuable 

 book more than once, and each time with considerable profit to 

 myself; still I cannot agree with all his conclusions. My paper on 

 the origin of the Lagoon called the Fleet is not as explicit as I 

 would wish, as I intended to point out that the sea-banks are due to 

 the principal currents, which are usually the incoming tidal currents. 

 In some places, as off the S.E. coast of Ireland, the prevailing winds 

 and incoming tidal currents act conjointly ; but west of Carnsore 

 point [the S.E. headland of Ireland] there are cross-tides, apparently 

 due to the curl round the Salter Islands : and here we find, at the 

 lagoon called Ballyteige mudlands, that the beach travels from 

 Crossfarnoge Point towards the W.N.W., although the prevailing 

 winds are from the S. W. and S.S.W. ; while on the coast of Mayo, be- 

 tween Killiney Bay and Clew Bay [a coast apparently most favourable 

 to the formation of bars and lagoons], the beach has no regular set, 

 but goes sometimes north, at other times south, or inland or seaward, 

 although there are on this coast nearly constant winds from between 

 the south and west, generally a few points off S.W. From what I 



