Tremadoc [Wales]
Sepr. 4. 1831
Dear Darwin
I left Capel Curig the day before yesterday & the stupid red nosed waiter did
not shew me your letter till a few hours before I started. Otherwise I should have
endeavoured to profit by your information respecting Cwm Idwal.
I ought however to have seen the madrepores; for last
wednesday I went from Capel Curig to Cwm Idwal and thence clambered out at the top by
the side of Twll Dy a very curious chasm which I suppose you have seen I then scaled the
crests of Glider Bach & G. Fawr and zig-zagged down to the Inn. Your
information did not however surprise me, as madrepores are quite as likely to be met
with as terebratulæ, which seem to occur here and there thro' ye
Snowdonian chain. I found terebratulæ among the talcose slates of Foel
Goch a precipice just to ye west of Cwm Idwal— I found organic
remains in ye slate of Moel Shabod, but did not stumble on any bed in
which they abounded. At first I found specimens about the middle of the great zone of
slate, & afterwards in the stone walls above the wood (by the way stone walls
are good localities for fossils and often tell us a good story
wh. it wd be difficult to make out without 'em).
I don't understand your puzzle about M. Shabod. Why
should not the rough beds at the bottom, on ye N.W. side, pass
under the blue slate with shells? I don't agree with you in thinking that the mass of
trap on ye crest of the hill is under the slate. It appears to
me decidedly to be over it— And in ye great Cwm with
ye small lake on ye East side we see the slate under
ye trap.— Again the trap wraps round in a horse Shoe shape to
ye S.E.—twists round to ye E. side of
the great Cwm, & then runs in a mass about 200 yards wide in a
directn. about N.E. for a mile or two, between two
great vertical masses of baked slate. E.G.,
[DIAGRAM HERE]
My picture is detestable and out of all gentlemanlike proportions but you must suppose
4 & 5 to be pulled out considerably to ye left hand of X
No.1 & No.2 are as in your letter;
No.3 ranges a mile to the S—. & then comes
round to No.5—the connexion is not ideal, as you may
walk all the way on trap from No.3 to No.5. The
slate No.4 where in contact is as hard as a flint. I'm beginning
to think that I shall not reach Barmouth this year. Therefore have the kindness to
address me at Carnarvon, which I shall for some time consider as my head
quarters—tho' I shall probably not often be there— To give you some
outline of my progress I will send you a skeleton of my walk.
21st. (this day fortnight) from Carnarvon to Dolbadarn; having in
ye morning heard a sermon an hour long & gone a geological
Sunday walk towards the S.— 22d. a
hardworking day along the Crown, Shoulders & ribs of Snowdon
23d. a still harder day, commencing with
ye slate quarries. (4 hours before Breakfast, what
wd your man have said to that?)—& then scaling Lidir
Mawr, & zigzagging along ye Crests of ye Chain to
Twll Dy, & so home in ye dusk
(24th. weather bound the whole day
(25th. hammer my way to Cap<el>
Curig—lunch, & then hammer my way to Tinny Maes— making
anot<her> modest collection of geological specimens.)
26th. Carnedd David, Carned Llewelyn, & so down the
rough crags of Porphyry (we saw at a distance) down to Aber—& thence
back to Tinny Maes. 27. ascertain the nature of ye beds below
the great slate zone by two or three traverses; & end at Bangor. 28. In
a great measure a day of rest—E.G. drive to Aber.
29th. To Conway by the crests of the hill—thence
across the water to ye ridges between great & little Orms head
Evg drive to Llanrwst.— 30th. Cross
the mountains on foot by the line of ye
lakes to Capel Curig.: caught in a mist and deluge of rain and steer over
ye mountains by Compass, reach the turnpike within a quarter of a mile
of ye road turning off to ye
Inn. 31 Lake Ogwen Glider Fawr & Bach, &c &c
to C. Curig. 1st Sepr The crest
& flanks of Moel Shabod— Evening excursion to ye knolls
N. of the trap &c. 2d. Mountains between
C. Curig and Llanrwst, & visit some of ye
mines— 3d. Bettws, Penmachno, Maentwrog, & Tremadoc,
ascending one or two hills by ye way. 4th.
Sunday, a day of rest—continual mist & rain.
My best regards to your friends at Shrewsbury. | Yours most truly A Sedgwick
P S. I saw no basalt at Lake Ogwen but a very black pyritous variety
of rock something between Lydian stone & compact felspar. It differs from basalt
in being extremely siliceous.— Perhaps I did not see the spot you mention.
I am going as soon as wind & weather permit to make traverses between
this place & Carnarvon. They will take 10 days
