188 Correspondence — Mr. W. M. Hutchings. 



resemblance to the schists with garnet and staurolite, and that the 

 authigenous minerals in them are neither garnet nor staurolite, but 

 some impure hydrons silicates. Dr. Heim's letter merely asserts the 

 contrary to my contentions, without adducing any fresh evidence. 



T. G. Bonnet. 



THE CULM-MEASURES AT BUDE, NOETH CORNWALL. 



Sir, — I have read with much interest the paper by Major-General 

 McMahon on the rocks at Bude. During one of two summer 

 visits to Tintagel I made a short stay at Bude, and saw the 

 extremely contorted strata so well described in the paper referred 

 to. Like the author of that paper, I was desirous of seeing what 

 amount of metamorphism had resulted from so much pressure and 

 dislocation, but expecting to pay a longer visit I took away only 

 two specimens. These were taken from two layers, a few inches 

 apart, of a very sharp fold exposed in a cove a little way south of 

 Bude Haven, — I think it was " Efford Ditch." One of the layers 

 was darker in colour, much softer, and more laminated than the 

 other. 



If any conclusions may be drawn from so limited a stock of 

 material (and macroscopically, at least, my specimens appeared fairly 

 representative of many of the rocks in this and other cliffs of the 

 district), the rocks of Bude are entitled to complain that they have 

 been made to appear as being less appreciative of, and as making 

 less return for, the large amount of force expended on them than is 

 really the case. 



The microscope shows the general structure and composition of my 

 specimens to be exactly as described by Major-General McMahon ; 

 but a close study of very thin portions of slides, under high powers, 

 shows a good deal more, especially in the harder of the two layers. 



In among the unaltered original clastic material may be seen a 

 considerable amount of rutile, perfectly distinct from any bits of that 

 mineral which may have come from older rocks. There are large 

 numbers of acicular crystals of it, vividly polarizing, as well as 

 countless minute dark rods, so well shown in many slates, etc. It 

 is also present in grains and granular aggregates, and in plates, 

 some of them of relatively large size. The total amount of it varies 

 much, even in slides from the same small piece, but it is always 

 considerable, and in one slide from the harder layer of rock it is 

 particularly abundant. This slide also shows a good many long 

 crystals of tourmaline (quite distinct from the clastic grains of that 

 mineral) and a good deal of secondary sericitic mica, some of it rich 

 in rutile crystals. Indeed, parts of this slide at once remind one of 

 some of the sericite-phyllites of the Tintagel rocks, in which the 

 rutile occurs in just the same manner ; and comparisons of the two 

 leave little doubt that some at least of the Bude strata have made a 

 good start towards the metarnorphisni which is so intense at 

 Tintagel. 



Of course it may be that my two specimens are exceptional, and that 

 Major-General McMahon did not chance on these or similar layers. 



