from the earth, and from its weight, much greater than that of air, forms a thick stratum of suffocating gas upon the floor of the cavern. When a man enters, his head and shoulders rise above the stratum of gas, and he breathes pure air; but when a dog is introduced, his head and body plunge completely into the carbonic acid gas, and he soon falls down, suffocated. The animal is then removed by the guide, laid upon the grass outside, and, in a short time, recovers.

Dr. Ozanam has shown that this suffocation by carbonic acid, when produced properly, affects a patient like chloroform, ether, or nitrous oxide, and can be made available in surgical operations. Indeed, he considers that carbonic acid has certain advantages over chloroform, and that it is less dangerous than the latter.

But of all the means hitherto employed to render man perfectly insensible to pain, the most curious, perhaps, is that called Hypnotism or Braidism, discovered many years ago by the late Dr. Braid, of Manchester, and practised successfully by him in England. It consists in placing some object, such as a cork or a piece of polished metal, at a short distance from the forehead of the patient, and requesting him to fix his eyes steadfastly upon it. After some time, which varies from a few minutes to half an hour or so, according to the constitution of the individual, the patient's eyes seem riveted upon the object in question, and for some moments he remains thus, without once closing them; they then suddenly close, and the patient falls into what is termed the hypnotic state, a kind of somnambulism similar to mesmerism. Consciousness has disappeared, and complete insensibility to pain has ensued.

Braid's discovery seems to have been abandoned for some time past by the medical world, but was occasionally put in practice by lecturers on the so-called "electro-biology," &c. Lately, however, it has been taken up again in Paris, by M. Paul Broca, surgeon to one of the hospitals of that city; and Dr. Braid just lived long enough to hear of his method of producing anesthesia meeting with singular success in the hands of M. Broca. One of the first results obtained by the latter was made known a year or so ago at the Académie de Médecine. It was the case of a woman who had repeatedly refused to be operated upon for a large tumour. At length, M. Broca induced anesthesia by causing the patient to fix her eyes upon a metallic disc which he held above her forehead. In about a quarter of an hour, a state of complete insensibility supervened, and the operation was performed. On returning to her senses, the poor woman would not believe that the operation had indeed taken place whilst she was under the influence of sleep.

mologist will find, both on the shores and inland, many interesting birds and insects.

To the shell-collector more especially, is this a locality of deep interest, for, about seven miles from Barmouth, in the direction of Harlech, there is a small tongue of land jutting into the sea, called Mochres, where shells of great rarity, both univalve and bivalve, are to be met with on the beach at low water, more particularly after tempestuous weather.*

And now, what have we for the geologist and mineralogist? Judging from the ecstasies of two learned professors from the metropolis, with whom we journeyed a few miles through this lovely district, as well as from our own observation, we should say that there are few parts of Britain which afford so many opportunities for the study of these subjects as do the hills and rocks of this neighbourhood.

The following extracts concerning the geology of Cader Idris will convey to the reader some idea of the varied character of the strata in this district :

:

"GEOLOGY.-It consists of silicious porphyry, quartz, and schorl, and is surrounded by slaty hills. Evidences of the volcanic character of the mountain are abundant. Numerous specimens of lava, pumice, and other volcanic products, have been discovered on the sides and base of the mountain. Columnar crystals of basalt are scattered in profusion about the summit and on some of the inferior cliffs, and particularly on one side, there are vast beds of porous stone, bearing evident marks of strong ignition and vitrification-some reduced to the state of slag, and others having the cellular appearance and lightness of pumice."-Black's Guide, p. 121.

"The slope of Cader, on the Talyllyn side, above Llynycae, is an igneous rock, principally composed of amygdaloidal green-stone, and under are masses of felspathic trap and long lines of green-stone, interbedded with altered slate, forming the steep north cliff of the mountain, and overlooking the high valley between the cliff and Llynygader, which itself is formed almost entirely of felspathic ash and conglomerate, with interbedded lines of green-stone-the whole dipping under the igneous rocks of the cliffs. Lingular flags underlie these."-Ramsay.

*For the guidance of conchologists visiting this interesting locality, we may add that Mochres may be approached from two points, namely, from Llanduwe, a church and inn, situated rather over four miles on the road from Barmouth to Harlech, or from Llanbedr, a considerable village, three or four miles nearer to Harlech, on the same road. Although a little may be saved in the distance, by approaching it from the first-named place, yet, on account of the tedious walk across a dreary moor which must be traversed, as well as the difficulty sometimes experienced in crossing to Mochres from the mainland by this route, we strongly recommend the tourist to proceed along the beautiful coast-road to the village last-named (Llanbedr), which is close to the peninsula, and from which he may reach the shell-covered beach in a few minutes without any difficulty.

Amongst the numerous mineral products extracted from the soil in various parts of the neighbourhood, the most conspicuous are slate, copper, lead, and gold; and, as reference has already been made to the last-named precious metal in a recent number of this periodical, we shall now add a few details on the subject, which may, perhaps, be interesting to our readers.

In his paper on the Gold Mines of this district, our contributor more than once mentioned the name of Mr. Readwin, to whose enterprise and scientific knowledge this country is indebted for the new mine of wealth which is being laid open in these our home-diggings.*

During our recent visit, we were so fortunate as to meet that gentleman, who is largely interested in several of the most important mines in the neighbourhood; and one of these, the Garthgill mine, we were permitted, through his kindness, to inspect.

Let us narrate the details of our visit.

Having received a note from Mr. Readwin, stating that he would be at the Garthgill mine, which is situated about halfway between Barmouth and Dolgelly, not far from the coachroad, between one and two o'clock in the afternoon, we started from the former place on a magnificent July morning, at about half-past eleven; and, after a smart five-mile walk, arrived at the "Halfway House," a little roadside inn, at a place called Pont Ddu, which is distant about one mile from the workings of the Garthgill mine.

A word en passant concerning this same walk of five miles. The road runs along the northern bank of the river, or, more properly speaking, the estuary of the Mawddach, deviating slightly, here and there, from the upward course of the stream; and, although we have visited many a beautiful scene, in Britain as well as abroad, we must confess that we have never met with anything to surpass this one. We see it before us in imagination as we write. Facing us, through a break in the trees, are the towering heights of Cader, on the opposite side of the river. To the right we have the boundless expanse of ocean peering through the bold headlands at the mouth of the estuary. To the left, the Mawddach, vying in beauty with the choicest portions of the Rhine, and presenting the appearance of a series of beautiful lakes through the windings of the stream amongst the mountains; whilst on all sides are ranges of hills, the slopes of some being fertile meadows, others bare, rugged, and precipitous, and others, again, concealed from the

* "The English California," by G. P. Bevan. No. IV. POPULAR SCIENCE REVIEW.

eye by the plantations of pine and fir, reaching from base to summit.

By the wayside are walls and hedges glowing with all the colours of the rainbow. Foxgloves of intense purple, wild roses of the deepest pink, with here and there wild geraniums, wild strawberries, and rasps; and as to the ferns, we feel, when we stoop to pluck a frond, to be used for driving off the troublesome flies, as though we were committing a desecration upon nature, in thus deforming the graceful cluster which shoots its arching stems on every side.

But we must quit this lovely scene, only, however, to approach another almost as beautiful. Having partaken of luncheon at the "Half-way House," a meal rendered most enjoyable by the healthful exercise of a rapid walk amongst these glorious scenes, we hastened onwards, and soon arrived at a large waterwheel, a mile beyond Pont Ddu, which is used for grinding the copper ore extracted from a neighbouring mine. Here we diverged from the main road, and, under the guidance of a blacksmith, who has a smithy hard by, and who was unable to speak a word of "Sassenach" (Saxon, or English), whilst we are equally well versed in "Cymraeg" (Cambrian, or Welsh), we found the "engine-house" of the Garthgill Mine. And here another beautiful scene presented itself to our gaze.

In the mining districts, the "Black Country" of Northumberland, Lancashire, and Staffordshire, nature appears to don sackcloth and ashes; to mourn, as it were, over the robberies hourly perpetrated in her domains. But here, amongst these lovely hills, she welcomes the enterprising miner, and tempts him to commence his operations by laying her treasures at his feet, and holding out to him every inducement that her charms can afford.

On the one hand, we find nought but smoke and arid desolation; and, if some unsuspecting plant, some blade of grass or tender floweret, should venture to extrude itself above the surface, the noxious gases of the furnace, factory, or mine, at once deprive it of its tints, and cause it soon to droop and die for very shame. Here, on the other hand, the elements and nature co-operate with man. The rushing waterfall, bubbling and gurgling amongst the rocks, stops in its headlong course, and, flowing gently through an artificial duct, assists to turn the wheel, and work the pestles of the miner; whilst the clear stream below serves at once to slake his thirst, to lave and cool his heated brow, and cleanse his ore from dross and from impurities.

'Twas such a scene as this that we encountered here.

From the "engine-house" (to be presently described), we continued to climb up the hill, accompanied now by the over

looker of the mine, and, after traversing a beautiful meadow on the mountain slope, where they were busy getting in the hay, and passing more than one working, at which operations had just been commenced, we suddenly found ourselves before the chief working or lode; not a very imposing, but still an interesting, excavation.

It is a small tunnel driven into the hill-side. Its height is about eight or ten feet, and its width barely five; and at the entrance we found several heaps of the auriferous quartz.

Entering the tunnel, we observed that the superincumbent rock and earth were supported by props and joists of wood; and, after penetrating about twenty or thirty yards, we found ourselves with the miners, who were busily engaged with pickaxe and gunpowder, procuring the gold-charged mineral, which, by the light of their candles, glistens with the precious metal it contains.

But it is a cold, damp burrow, this treasure-yielding vault! Through the grey rock the wet trickles as in some cave of stalactite, and under-foot we find a pool of water.

The miners had just finished procuring a load of the quartz, and were boring for a fresh blast. After watching them for a time, we retraced our steps, and once more emerged from the damp chill cavern into the genial sunshine, and feasted our eyes upon the glorious hills and valleys of the Mawddach.

Arrived once more at the "engine-house," a little wooden shed containing the apparatus used for grinding the quartz, we met the enterprising owner of the mine, who described to us the process and machinery by which the precious metal is extracted from the crude mineral.

We shall, however, refrain from employing the technical phraseology used by our instructor, but shall seek to convey the information after our own fashion.

Just let the reader join us whilst we indulge in a stretch of the imagination. He must suppose that our skilful companion, the proprietor of the mine, who knows so well how to conjure up the treasures from the bosom of these hills, is also able, through some potent spell, to summon the presiding Genius of the place (one of those Welsh giants, in whom the country people still believe, and whose footsteps they will show you, thirty feet apart *), and having done so, places before him a pestle and mortar, of proportions suited to his strength, and by his side a heap of auriferous quartz, with a quantity of quicksilver, bidding

* On the coach-road between Beddgelert and Carnarvon, the impress of one of the feet of a giant has been painted on the top of a rock on one side of the road, and that of the other foot on the opposite side, distant about thirty feet.

VOL. II.-NO. V,

D