356 



Fichtelgebirge and with the kersantites and ininettesW of South 

 Thuringia and the Frankenwald. 



The following analyses, with the exception of the first, were made 

 by Mr. COLLINS. 



99-81 100-19 100-01 99-06 98-38 99-67 99-75 99-28 99-24 100-25 

 Sp. Gr. 2-70 2-73 2-75 2-50 2-75 2'46 2-66 2-54 2-72 



I. Augite-minette. Trelissick Creek. Analysis by Mr. PHILLIPS. 



II. Lamb Creek, near Truro. 



III. Nare Point, near Porthalla. 



IV. Nare Point, near Porthalla. This is stated by Mr. COLLINS to be part of the same 



mass as that which yielded Analysis III. 



V. New Quay. Contains also '32 of PuOs. 



VI. Fiddler's Green Dyke. 



VII. Flushing. 



VIII. The Gannel. Contains -20 of P 2 5 . 



IX. Roscreage, near the foot of the Beacon. 



X. Beacon Hill, Falmouth. 



The first three analyses represent the composition of the normal 

 mica-traps ; the remaining analyses were made from weathered 

 specimens. Mr. COLLINS states that all the rocks contain phosphoric 

 acid, manganese, lithia and fluorine. Speaking of their physical 

 characters, he says : " The rocks vary in colour from golden yellow 

 to greyish or chocolate brown, with often a purplish tinge in the 

 hardest parts when freshly broken. Near the surface they are often 



much decomposed When the rock is undecomposed its 



appearance is unmistakable, whether fine or coarse grained ; where 

 the decomposition is but slight, it often simulates to a cursory view 



a brown sandstone, for which, locally, it is often mistaken 



A tendency to spheroidal structure developed by decomposition may 

 generally be observed." 



The author is indebted to Mr. COLLINS for a specimen from the 

 Helford River. It is a medium-grained rock in which the two principal 

 constituents, a dark mica and a pink felspar, can be easily recognized 

 with a lens. The examination of a thin section shows that the matrix 

 of the rock in which the other constituents are embedded is a coarse- 

 grained aggregate ofc unstriated felspar. Notwithstanding the presence 

 of considerable quantities of ferrite and calcite-dust the grains retain 



1 1) R. POHLMANN. Uber Glimmer-diorite und Kersantite Siidthuringens und des Franken- 

 waldes. N. J. Beilage Band III. (1885), p. 67. 



