BKITISH ISLES. 17 



Other ores than tin occur. The proportion^ of tin-ore in one of the 

 newest works scarcely exceeded that in one of the poorest lodes ; but 

 the 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 tilled with sand and clay. The bed 

 that rests on it is scarcely distinguishable from it, except that its ingre- 

 dients 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 upland 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 vertical distances from the *nin-ground" 

 both north and south of the watershed. 



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 freshwater with saltwater deposits. 



Detitral 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 Cligger 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 footnotes, giving references to 

 the many works on the district. W. W. 



Hicks, H. On the Arenig and Llandeilo llocks of St. David's. Rep. 

 Brit. Assoc, for 1873, Sections, p. 82. 



This paper is a continuation of a previous one, and completes the de- 

 scription to the top of the Llandeilo series. The Lower Aren'uj series 

 occurs as black slates and flags, about 1000 feet thick ; and it con- 

 tains many species of dendi-oid Graptolites and Trilobitcs peculiar to 

 this group. The Upper Areniy series occurs as fine-grained, soft, black 

 shales, 1000 feet thick ; and all the fossils are distinct. The Lower 

 Llaiicleilo series consists of black slates and hard grey flaggy sandstones 

 with siliceous schist and beds of felspathic ash at the lower part, and of 

 dark slates and flags with many calcareous bands in the upper part ; 

 about 1500 feet thick. The Upper Lhmdeilo series consists of black 

 slates and flags, several thousand feet thick. 



All these divisions are conformable with each other. The author 

 1874. c 



