Correspondence — Professor E. Sull. 139 



confirm Weigand so far as this is concerned. It must be remem- 

 bered that Weigand's paper appeared in 1875, at a time when the 

 notion that all serpentines were altered olivine-rocks was becoming 

 very genei'al in consequence of the researches of Sandberger and 

 Tscherraak, published some eight or nine years previously. 



I may take this opportunity of referring to Col. McMahon's 

 paper in the same number of the Geological Magazine. I have 

 no new facts of any importance to add on the subject referred to, 

 and I do not think that any useful purpose would be served by my 

 attempting to remove the objections raised by Col. McMahon. 

 I cannot explain why foliation has been developed in some cases 

 and not in others. The apparently capricious manner in which 

 foliation comes in is equally striking in the Scourie Dyke and in 

 the Lizard gabbros. If I am right in one case, I am right in the 

 other ; and if I am wrong in one case, I am wrong in the other. 

 I believe with Col. McMahon that foliation may be produced in 

 connexion with the intrusion of plutonic rocks ; but I cannot 

 explain the foliation of the Lizard gabbros in this way. 



Col. McMahon quotes Prof. Bonney as saying that the serpentine 

 is "free from all signs of disturbance." This is true of the serpen- 

 tine locally, as it is of the gabbro ; but it is not true generally. There 

 are the same signs of disturbance in the serpentine as there are in 

 the gabbro. I have a polished slab of serpentine from Porthalla, 

 which shows precisely the same structural features as the figured 

 slab of augen-gabbro from Karakclews. Abundant signs of 

 pressure metamorphism occur also in the serpentine near Mullion 

 Cove. J. J. H. Teall. 



BORING AT BLETCHLET. 



SiK, — The London and North- Western Eailway Company have for 

 some time been carrying out a trial-boring for water ; and if they have 

 not found what they were in search of, they have made a discovery 

 whicli is interesting to geologists in reference to the underground 

 structure of the central and eastern parts of England. 1 have not 

 yet the full details before me ; but, from the information furnished by 

 Mr. C. Bowen Cooke, it would appear that the boring-rods, after 

 penetrating the Jurassic Clays (called by my informant the " Oxford 

 Clay "), struck on a very hard rock, of which three small specimens 

 were sent to me for identification. On examining them I had no 

 difficulty in giving a reply. The specimens appear to consist of 

 finely-crj'stalline quartz-felsite, with some green mica, and evidently 

 form a portion of the old Pre-Triassic ridge, which, as all under- 

 ground borings combine to prove, underlies the Mesozoic formations 

 of this part of England. 



I hope ere long to have a complete series of the cores brought up 

 from the boring, and to be able to give fuller details. 



Geol Survey of Ireland, Edward Hull. 



14, Hume Street, Dublin. 



