74 Col. McMahon — On the Lizard Gabhro. 



common, though B. ultimus occurs sometimes ; it is true that all 

 three are often regarded as varieties of one species, but that makes, 

 no difference to the fact of the two varieties being specially character- 

 istic of the Gault. 



Ostrea acutirostris has not, I believe, previously been found below 

 the Chalk Marl, but it is not a common shell anywhere, and is 

 believed to occur in Upper as well as in Lower Chalk, so that it is 

 evidently a species which has a long range. 



The statement that Ostrea vesicularis has not been discovered 

 below the Chalk is quite erroneous, for it is a common shell in the 

 Upper Gault of Folkestone and elsewhere. 



(3) Lastly, the clay above the "coproiite bed" at West Dereham, 

 has the lithological characters and general appearance of Gault. It 

 is by no means unusual for the lower part of the Gault to contain 

 fossils in the form of phosphate casts, more or less rolled and worn ;. 

 such phosphatized fossils are particularly abundant within twenty 

 feet of the base of the Gault in Buckinghamshire, and in the same 

 county the passage-beds between the Gault and Lower Greensand 

 often contain large lumps of sandy phosphate, which resemble those 

 of the junction-bed at West Dei'eham. There is nothing therefore 

 in the character or contents of the West Dereham clay that is incom- 

 patible with its being true Gault. For the reasons above stated we 

 must maintain that all the previous authors were right in accepting 

 the sections near West Dereham as proving the existence of Gault in 

 that part of West Norfolk. How much farther north the Gault ex- 

 tends is another question which we are endeavouring to ascertain, 

 and such evidence as we can obtain will be embodied in a paper 

 which we intend to bring before the Geological Society. We shall 

 also endeavour to accoimt for the apparent passage between the Gault 

 and the Chalk Marl; but we may remark that at Shouldham we 

 found what appears to be the true glauconitic base of the latter, 

 above the clay which Mr. Eeid describes as containing Belemnites 

 and Plicatula. 



[F ostscrvjpt. — Since the above was written we have had a boring 

 made in the quarries at Stoke Ferry to a depth of fifty-five feet, and 

 have proved the existence of a bed of Chloritic Marl at the base of 

 the Chalk Marl, and resting on blue clay ; the total thickness of the 

 Chalk Marl there is seventy-three feet, and it must be remembered 

 that below this there is at least sixty feet of Gault.] 



VL — Note on the Foliation of the Lizakd Gabbed. 

 By Colonel C. A. McMahon, F.G.S. 



THE appearance of Professor Bonney's letter in the December 

 Number of the Geological Magazine, in which he suggests that 

 Mr. J. J, Harris Teall's proposed explanation of the cause of the 

 foliation of the Lizard gabbro " ought to be regarded as an hypothesis, 

 on its probation, and should not be quoted as an undoubted fact," 

 emboldens me to offer some remarks on the subject. 



Mr. Teall suggests that the " foliation in the Lizard gabbro is the 



