178 Notices of Memoirs — W. J. JELenwood — Detrital Tin-ore. 



lodes, but tlie metal from the stream-ore is the best. Gold has been 

 found, but very sparingly, in the detritus of every tin-district. 



The blocks and smaller fragments on the tin-ground show marks 

 of abrasion, and the interstices are filled with sand and clay. The 

 bed that rests on it is scarcely distinguishable from it, but that its 

 ingredients are perhaps less abraded, and that it is almost destitute 

 of tin-ore. The bed next above this has a likeness in 'neighbouring 

 valleys, and yet sometimes differs in different parts of the same 

 valley : it seems that after the tin-ground was deposited timber 

 sometimes flourished in the lower valleys, and brushwood in the up- 

 land glens, subsequent change in the relative levels of land and sea 

 affecting the former more than the latter ; and that the deposit of 

 barren debris was once or twice interrupted by a large formation of 

 peat. Vegetable remains of the same kind occur within short verti- 

 cal distances from the " tin-ground " both north and south of the 

 water-shed. 



The deep valleys which formerly opened to the sea below high- 

 water mark, on the south coast, contain alternations of mineral with 

 vegetable matter, and of fresh- water with salt-water deposits. 



In the shallow stream- works of the moorlands the upper parts con- 

 sist of much the same ingredients as the neighbouring rocks, are like 

 the beds of the neighbouring brooks, and are disposed in thin layers 

 with clay-partings. 



Detrital tin- ore does not occur only (though chiefly) in the low 

 grounds, but has also been found in abraded masses on the slopes of 

 hills, whence it has been traced to the parent lodes. 



If detrital tin-ore has also been deposited in the sea, it must be 

 covered, as on land, by more recent deposits, soundings having failed 

 to find it. At digger Head the ore derived from the waste of the 

 cliffs is collected. 



The paper concludes with three tables, giving the composition of 

 the tin-ground and of the adjoining and neighbouring rocks, the 

 comparison of vegetable remains in the upper and lower parts of the 

 same and of different valleys, and the mineral composition and 

 organic contents of the beds laid open in various stream-works. 



Throughout is a very large number of foot-notes, giving references 

 to the maoy works on the district, W. W. 



YI. — Bkief Abstracts. ^ 



1873. 

 Greenfell, J. G. StreptorJiyncus Kellii. Trans. Clifton Coll. Sci. 

 Soc, part iv. ;^p. 16, 17. 

 The shells were found in an "Oolitic" Limestone, from the lower 

 part of the Carboniferous Limestone (above the Black Eock), at the 

 foot of the gully down to the river from the Downs, and are im- 

 portant as showing that StreptorJiyncus Kellii of McCoy is only a 

 variety of tS. crenistria, as suggested by Davidson. The deep mesial 

 furrow and the rounded cardinal angles were the points on which 

 .McCoy chiefly insisted as specific differences, and in one of these 

 specimens the former character occurs with acute cardinal angles, 



