parts not less than thirty, and even forty. In many places there is a liquor continually dropping from it, which congeals immediately, and forms a species of transparent stone, but not so fine and clear as rock crystal. As we continued our peregrination, we thought ourselves in no small dauger from the roof, which we found but indifferently propped in some places with wood much decayed, Under the houses, and many of the streets, however, it seemed to be tolerably secured by immense stones set in mortar; in other parts, where there are only fields or gardens above, it was totally unsupported for a considerable space, the roof being perfectly level, or a plane piece of rock.

After traversing about two miles, we again descended about twenty steps, and here found some workmen, in a very cold and damp place, propping up a most dangerous part, which they were fearful would give way every moment. We were glad to give them money for some drink, and make our visit at this place as short as possible. The path here is not more than three feet in width, and the roof so low, that we were obliged to stoop considerably,

By this time several of the party began to repent of their journey, and were much afraid of the damp and cold air we frequently experienced. But, alas! there was no retreating.

On walking some little distance farther, we entered into a kind of salon, cut out of the rock, and said to be exactly under St. James's church. This was illuminated with great taste, occasioned an agreeable surprise, and made us all ample amends for the danger and difficulty we had just before gone through. At one end was a representation in miniature of some of the principal forts in the Indies, with the fortifications, draw-bridges, &c. Cannons were planted, with a couple of soldiers to each, ready to fire. Centinels were placed at different parts of the garrison, particularly before the governor's house; and a regiment of armed men was drawn up in another place, with their general in the front. The whole was made up of a kind of clay which the place affords, was ingeniously contrived, and the light that was thrown upon it, gave it a very pretty effect,

On the other side of this hall, was a long table set out with cold tongues, bread and butter, and some of the best Burgundy I ever drank, Now every thing was hilarity and mirth; our fears were entirely dispelled, and the danger we dreaded the moment before was now no longer thought of. In short, we were all in good spirits

1

again, and proceeded on our journey about two miles farther, when our guides judged it prudent for us to ascend, as we were then got to the steps which lead up to the town. We here found ourselves safe at the Val de Grace, near the English benedictine convent, without the least accident having happened to any one of the party. We imagined we had walked about two French leagues, and were absent from the surface of the earth, betwixt four and five hours.

After we had thanked the inspectors and guides for their very great civility, politeness, and attention, we took our leave to visit the English benedictines convent, in whose court-yard, and within a few yards of their house, the roof of the subterraneous passage had given way, and fallen in, the depth of one hundred and ninety-three feet.

Though there were some little danger attending our rash expedi tion (as some people were pleased to term it), yet it was most exceed. ingly agreeable, and so perfectly a novel scene, that we were all highly delighted, and thought ourselves amply repaid for our trouble.

I regretted much that I did not take a thermometer and barometer down with me, that I might have had an opportunity of making some remarks on the temperature and weight of the air. Certainly, however, it was colder at this time than on the surface of the earth. But Mr. Smeathman informed me, that when he descended the last winter, in the long and hard frost, he found the air much more temperate than above ground, but far from warm. Neither, however, had he a thermometer with him. I lamented too that I had not time to make more remarks on the petrefactions, &c.

Mr. Smeathman observed, that when he descended, he found a very sensible difficulty of breathing in some of the passages and caverns, where the superincumbent rock was low, and the company crowded. This no doubt was much increased by the number of persons and of wax-lights, but he does not apprehend that the diffi culty would have been so great in rooms of equal dimensions above ground. We remarked too, when we descended, that there was, in some degree, an oppression of respiration throughout the whole passage.

There were formerly several openings into the quarries, but the two I have mentioned, viz. the Observatory, and the Val de Grace, are, I believe, the only ones left; and these the inspectors keep con

stantly locked, and rarely open them, except to strangers particularly introduced, and to workmen who are always employed in some part by the king.

The police thought it a necessary precaution to secure all the entrances into this cavern, from its having been formerly inhabited by a famous gang of robbers, who infested the country for many miles round the city of Paris.

As to the origin of this quarry, I could not, on the strictest enenquiry, learn any thing satisfactory; and the only account I know published, is contained in the Tableaux de Paris, tom premier, chap. v. p. 12.

"For the first building of Paris, it was necessary to get the stone in the environs, and the consumption of it was very considerable. As Paris was enlarged, the suburbs were insensibly built on the ancient quarries, so that, all that you see without is essentially wanting in the earth, for the foundation of the city: hence proceed the frightful cavities, which are at this time found under the houses in several quarters. They stand upon abysses. It would not require a very violent shock to throw back the stones to the place from whence they have been raised with so much difficulty. Eight men being swallowed up in a gulph one hundred and fifty feet deep, and some other less known accidents, excited at length the vigilance of the police and the government, and, in fact, the buildings of several quarters have been privately propped up; and by this means, a support given to these obscure subterraneous places, which they before wanted.

"All the suburbs of St. James's, Harp-street, and even the street of Tournon, stand upon the ancient quarries; and pillars have been erected to support the weight of the houses. What a subject for reflections, in considering this great city formed, and supported by means absolutely contrary! These towers, these steeples, the arched roofs of these temples are so many signs to tell the eye, that what we now see in the air, is wanting under our feet."

[Memoirs of the Manchester Society, Vol. II.]

CHAP. XXVI.

MOSSES, MOORS, rogs, and THE PRODUCTION OF PEAT.

SECTION 1.

Introductory Remarks.

THE great abundance in the colder parts of the earth of vegetable quagmires or mosses, so denominated from the class of plants of which they chiefly consist, and the rapidity with which under certain circumstances they are renewed, while in the torrid zone they are totally wanting, are circumstances claiming the close attention of geologists. Pit-coal, in like manner, abounds in cold climates; but has, perhaps, never been found in the torrid zone. Hence the opinion entertained by some that mosses by length of time, and by being exposed to considerable pressure, are converted into pit-coal, has at least some little plausibility in its favour. That peat is entirely of vegetable origin cannot be doubted; that it consists chiefly of sphagnum palustre, or common bog-moss, and other similar plants which delight in moisture, is probable, and that it is formed by the action of water on dead vegetable matter, appears abundantly evident. But an accurate explanation of the suite of changes which take place during the formation of peat has not been given. A precise chemical examination of peat, and a comparison of its different varieties with those of pit-coal, would be a valuable addition to geological knowledge*. In the mean time it cannot be doubted that

* Dr. Thomson asserts, that he has made some experiments on the subject, but never could find any of the constituents of peat, mentioned by Dr. Rennie in his work on peat, in any of the varieties of that combustible which he was able to procure. He has examined peat from Lancashire, from Perthshire, from the neighbourhood of Stirling, from the neighbourhood of Edinburgh, and from a moss between Stirling and Glasgow. Dry peat is tasteless and insoluble in water. But if you steep it in water for several months it tinges the liquid reddish brown, similar to moss water. In water thus tinged he never could detect any thing by reagents, except some slight traces of vegetable extractive.

mosses act a very important part in nature, and that they afford us the means of detecting many curious changes which have taken place process of time on the surface of the earth.

in

Mosses always occur on plains, though these are frequently situated at some considerable height on the side of a mountain. They are always in the neighbourhood of ground higher than themselves, and are obviously the receptacle of water collected from neighbouring acclivities. They frequently contain many large trees, chiefly oak and fir, and this even in countries where trees will no longer grow, as the Orkneys and Western Islands of Scotland*. There is in an early number of the Philosophical Transactions a very valuable paper on the origin of mosses, by the Earl of Cromartie. And this nobleman, who was about the age of eighty when he wrote, had the singular good fortune to witness with his own eyes all the different steps of the process within a period of rather less than fifty years. [Thomson's Hist. of Royal Society.]

Mosses, in consequence of their low position, are frequently overflowed by torrents from adjoining hills and higher grounds; and when the soil below has been spongy and cavernous, particular parts of them have often been found to tremble aud move about like a boat on the water, and not unfrequently the whole range of moor or moss has sunk abruptly to a very consi derable depth below its former level; and hence, in many instances, the origin of extensive lakes. Thus in Finland, no later than 1793, a piece of ground approaching to this description, of four thousand square ells, sunk to a depth of fifteen fathomst: and in like manner a swampy seat in Norway, called Borga, in 1702, was transformed into a lake of not less than a hundred fathoms deep. The Philosophical Transactions abound with similar instances, of which it may be sufficient to notice the following: an extraordinary subsidence of a part of the cliffs or high grounds near

* The reason why wood does not grow in these places is not any change of the climate for the worse, but an increase of the number of sheep and cattle, which prevent trees from propagating themselves by seeds, the only way in which forests can be continued in a cold climate. Young trees brought from a distance and planted are sure to die.

+ Götting. Taschencalendar, 1795.