40 
THE GKOLOGIST. 
members, five shillings a-year. All meitibers will be entitled to copies of whatever 
printed minutes of the proceedings of the Asst>ciation are issued. The first meet- 
ing of tlie Association for business, will be held on an early day in January, which 
will be duly aimnunced to subscribers, and when an inaugural address will be 
delivereil by the Chairman. 
Chalk Sponhes of Yorkshire. — " Sir, — I think a paper, accompanied by 
sketches, of the sponges from the chalk of Flamborough Head, would be very accept- 
able to many of your readers. I do not find them described in any of the popular 
books, although probably they are to be found figured in some of the works on 
Yorkshire. — Yours, &c., X. V." 
Mammalian Remains near Wells. — " Sir, — Seeing in one of your maga- 
zines of this year a request that Geologists would furnisli you with the localities 
where the remains of mammals have been observed in the jirovinces, I beg to 
inform your reailers that I found several teeth of Rliinoceros and of Elephants on 
the side of the Mendip Hills, about two miles from the city of Wells, and close to 
the celebrated Wokey Hole cavern ; they were about fifteen feet below the surface, 
in a conglomerate resting on the dolomite limestone. — Yours, &c., Francis 
Drake, Leicester." 
Manner of octtinq Films of Selenite. — (See Vol. I. p. 444.) — " Good, large 
crystals of selenite can be split into lamina; of uniform thickness with a penknife ; 
but much care is rcquiretl, and many feilures occur. This is the method I have 
always employed for my own purposes, with sufficient success. — H. C. Sorby." 
Mineral-Veins. — (See Vol I. p. 4.'50.) — " If a portion of limestone be placed in 
the solution of any salt of the peroxide of iron, or a salt of the pn^toxide exjwsed 
to the air, a deposit of the peroxitle of iron is formed on the limestone. No such 
effect is produced by a fragment of sandstone ; and, in some cases, at all events, 
this will, I think, explain what your correspondent refers to. — H. C. Sorby." 
Mineral-Veins in Limestones and Sandstones. — "Dear Sir, — Inreply'to 
the very candid request of your correspondent, I beg to say, that the examples 
which have led me to arrive at the conclusion that mineral-veins, in. general, 
contain more iron in limestone than in siliceous strata, are those afforded in the 
lead-mining district of the north of England ; more i)articularlv in that part of it 
comprising Alston iNIoor, Allandale, and Weardale. The lead-bearing strata in 
these localities are of the mountain-limestone series, and consist of alternating 
members of calcareous, siliceous, and argillaceous characters. Interstratified with 
these beds is one of basalt, locally called the great whin-sill, and of considerable 
thickness, amounting in some jilaces to 30 or 40 fathoms, or even more. Higher 
up in the series is another of the same nature, which may be observed in the Wear 
Valley lietween StanlK)pe and Eastgate, but this seems to be of very linnted extent. 
The great whin-sill lies at a considerable depth below the surface in Weardale, 
nevertheless, it has been sunk through at Pasture Grove mine, where a very 
productive vein is being worked. It has also been penetrated at Slit mine, near 
Westgate. The workings of these two mines above and below the water-drainage 
lay open a very consideral)le thickness of strata. Owing to the rise of the beds m 
a westerly direction, the same sills which have to be sunk into in Weardale are 
accessible by adits at Alston Moor. The thickness of strata from the ujiper 
surface of the great whin-sill to the top of the lead-measures is about 180 fathoms. 
In this space are included 10 beds of limestone, 27 of sandstone, 29 of plate, 3 of 
an argillo-siliceous nature, and 5 of suli)hureous coal : the aggregate thickness of 
each set being as follows, namely, limestone 17!) ft., sandstone 345 ft., plate 414 ft., 
argillo-siliceous beds 147 ft., and coal 5 ft. Although these strata do not maintain 
a perfect uniformity of tliickness throughout, yet, the atiove may be taken as 
approximating to accuracy sufficiently for the present jiurjiose. The limestones and 
sandstones are the chief metalliferous strata, and, in the above section, the thick- 
ness of the former to that of the latter is as 1 to 191, without including the sili- 
ceous in the argillo-siliceous beds. The argillaceous strata are seldom productive 
of lead-ore, except in some veins which carry a rider, or vein-stone, where they are 
said to be mineralized. Dividing the lead-measures which lie above the whin-sill 
into three divisions, the middle is the richest and most exten.sively worked. From 
long experience in working these mines, it has been noted as a fact, that the veins 
