PHILOSOPHICAL PAPER S. Mr. ANDERSON'S ACCOUNT of a BITUMINOUS LAKE or PLAIN, in the Inland of TRINIDAD. [From the Seventy-ninth Volume of the PHILOSOPHICAL TRANS A ACTIONS.] Moft remarkable production of nature in the inland of Trinidad, is a bituminous lake, or rather plain, known by the name of Tar Lake; by the French called La Bray, from the refemblance to, and anfwering the intention of, fhip-pitch. It lies in the leeward fide of the island, about half-way from the Bocas to the fouth end, where the mangrove fwamps are interrupted by the fand-banks and hills; and on a point of land which extends into the fea about two miles, exactly oppofite to the high mountains of Paria, on the north fide of the Gulf. "This cape, or head-land is about fifty feet above the level of the fea, and is the greateft elevation of land on this fide of the island. From the fea it appears a mafs of black vitrified rocks; but, on a clofe examination, it is found a compofition of bituminous fcoriæ, vitrified fand, and earth, cemented together; in fome parts beds of cinders only are found. In approaching this cape, there is a strong fulphureous fmell, fometimes difagreeable. This fmell is prevalent in many parts of the ground to the distance of eight or ten miles from it. "This point of land is about two miles broad, and on the eaft and weft ûdes, joined to the main land on the south by the continuation of the mangrove fwamps; fo that the bitumi. nous plain is on the highest part of it, and only feparated from the fea by a margin of wood which furrounds it, and prevents a diftant profpect of it. Its fituation is fimilar to a favannah, ard, like them, it is not feen till treading upon its verge. Its colour, and even furface prefent at first the afpect of a lake of water; but I imagine it got the appellation of Lake when feen in the hot and dry weather, at which time its furface to the depth of an inch is liquid; and then from its cohefive quality it cannot be walked upon. "It is of a circular form, and I fuppofe about three miles in cir cumference. At my firft approach it appeared a plane, as fmooth as glafs, excepting fome fmall clumps of fhrubs and dwarf-trees that had taken poffeffion of some spots of it; but when I had proceeded fome yards on it, I found it divided into areola of different fizes and shapes: the chafms or divifions anastomost d through every part of it; the furface of the areola perfectly horizontal and smooth; the margins undulated, each undulation enlarged to the bottom till they join the op halfcm the diftance of about pofite. On the furface the margin from the fea, falls with a gentle declivity to it, and is or firft undulation is distant from the oppoft from four to fix feet, and and the fame depth before they coalefce; but where the angles of the arcolæ oppofe, the chaims or ramifications are wider and deeper. When I was at it, all these chafms were full of water, the whole forming one true horizontal plane, which rendered my invefligation of it difficult and tedious, being neceffitated to plunge into the water a great depth in pafling from one areola to another. The trueft idea that can be formed of its furface will be from the areola and their ramifications on the back of a turtle. Its more common confiftence and appearance is that of pit-coal, the colour rather greyer. It breaks into fmall fragments, of a cellular appearance and gloffy, with a number of minute and fhining particles interfperfed through its fubftance; it is very friable, and, when liquid, is of a jet black colour. Some parts of the furface are covered with a thin and brittle scoria, a little elevated. As to its depth, I can form no idea of it; for in no part could I find a fubftratum of any other fub france; in fome parts I found calcined earth mixed with it. "Although I fmelt fulphur very ftrong on paffing over many parts of it, I could difcover no appearance of it, or any rent or crack through which the fteams might iffue; probably it was from fome parts of the adjacent woods: for although fulphur is the bafis of this bituminous matter, yet the fmells are very different, and eafily diftinguished, for its fmelt comes the neareft to that of pitch of any thing I know. I could make no impreffion on its furface without an axe : at the depth of a foot I found it a little fofter, with an oily appearance, in fmall cells. A little of it held to a burning candle makes a hiffing or cracking noife. like nitre, emitting fmall fparks with a vivid flame, which extinguishes the moment the candle is removed. A piece put in the fire will boil up a long time without fuffering much diminution: after a long time's fevere heat, the furface will burn and form a thin fcoria, under which the reft remains liquid. Heat feems not to render it fluid, or occupy a larger space than when cold; from which, imagine, there is but little alteration on it during the dry months, as the folar rays cannot exert their force above an inch below the furface. I was told by one Frenchman, that in the dry feafon the whole was an uniform smooth mass; and by another, that the ravins contained water fit for ufe during the year; but neither can I believe: for" if, according to the firft affertion, it was an homogeneous mafs, fomething more than an external cause inuft affect it, to give it the prefent appearances: nor without fome hidden caufe can the fecond be granted. Although the bottoms of these ramified channels admit not of abforption, yet from their open expofure, and the black furface of the circumjacent parts, evaporation must go on amazing quick, and a fhort time of dry weather muft foon empty them; nor from the fituation and structure of the place is there a poffibility of fupply but from the clouds. To fhew that the progrefs of evaporation is inconceivably quick here, at the time I vifited it, there were, on an average, twothirds of the time inceffant torrents of rains; but from the afternoon being dry, with a gentle breeze (as is generally the cafe during the rainy feafon in this ifland), there evidently was an equilibrium between the rain and the evaporation; for in the courfe of three days i faw faw it twice, and perceived no al teration on the height of the water, nor any outlet for it but by evapo ration. "I take this bituminous fubftance to be the bitumen afphaltum Linnæi. A gentle heat renders it ductile; hence, mixed with a little greafe or common pitch, it is much ufed for the bottoms of fhips, and for which intention it is collected by many; and I fhould conceive it a prefervative against the borer, fo deftructive to fhips in this part of the world. "Befides this place, where it is found in this folid ftate, it is found liquid in many parts of the woods; and at the distance of twenty miles from this about two inches thick, round holes of three or four inches diameter, and often at cracks or rents. This is confequently liquid, and fmells ftronger of tar than when indurated, and adheres ftrongly to any thing it touches; greafe is the only thing that will diveft the hands of it. "The foil in general, for fome distance round La Bray, is cinders and burnt earths; and where not fo, it is a strong argillaceous foil; the whole exceedingly fertile, which is always the cafe where there are any fulphureous particles in it. Every part of the country, to the diftance of thirty miles round, has every appearance of being formed by convulfions of nature from fubterraneous fires. In feveral parts of the woods are hot iprings; fome I tried, with a well graduated thermometer of Fahrenheit, were 20° and 22 hotter than the atmosphere at the time of trial. From its pofition to them, this part of the island has certainly experienced the effects of the volcanic eruptions, which have heaped up thofe prodigious maffes of mountains that terminate the province of Paria on the north; and no doubt there has been, and still probably is, a communication between them. One of thefe monntains oppofite to La Bray in Trinidad, about thirty miles diftant, has every appearance of a volcanic mountain: however, the volcanic efforts have been very weak here, as no traces of them extend above two miles from the fea in this part of the island, and the greater part of it has had its origin from a very different cause to that of volcanos; but they have certainly laid the foundation of it, as is evident from the high ridge of mountains which furrounds its windward fide to protect it from the depredations of the ocean, and is its only barrier against that over-powering element, and may properly be called the fkeleton of the island. "From every examination I have made, I find the whole island formed of an argillaceous earth, either in its primitive ftate, or under its different metamorphofes. The bafes of the mountains are compofed of fchiftus argillaceus and talcum lithomargo; but the plains or lowlands remaining nearly in the fame moift ftate as at its formation, the component particles have not experienced the viciffitudes of nature fo much as the more elevated parts, confequently retain more of their primitive forms and properties. As argillaceous earth is formed from the fediment of the ocean, from the fituation of Trinidad to the continent, its formation is eafily accounted for, granting first the formation of the ridge of mountains that bound its windward fide, and the high mountains on the continent that nearly join it for the great influx of currents into the gulf of Paria from the coafts of Brazil and Andalufia muft bring a vast quantity of light earthy parti cles cles from the mouth of the numerous large rivers which traverfe thele parts of the continent; but the currents being repelled by thefe ridges of mountains, eddies and smooth water will be produced where they meet and oppofe, and therefore the earthy particles would fubfide, and form banks of mud, and by fresh accumulations added, would foon form dry land; and from thefe caufes it is evident fuch a tract of country as Trinidad muft be formed. But these causes, still exift, and the effect from them is evident; for the island is daily growing on the leeward fide, as may be feen from the mud-beds that extend a great way into the gulf, and there conftantly increase. But from the great influx from the ocean at the fouth end of the island, and its egrefs to the Atlantic again, through the Bocas, a channel muft ever exift between the continent and Trinidad." ACCOUNT of the CULTIVATION of LA C, by Mr. ROBERT SAUNDERS, Surgeon, at Boglepoor in Bengal. 16 AS [From the fame Work.] S lac is the produce of, and a staple article of commerce in Affam, a country border ing on and much connected with Thibet, fome account of it may not be an improper fupplement to the above remarks. "Lac is, ftrictly speaking, neither a gummy nor refinous fubftance, though it has fome properties in common to both. Gums are foluble in water, and refins in fpirits; lac admits of a very difficult union with either, without the mediation of some other agent. "Lac is known in Europe by the different appellations of tick lac, feed lack, and fhell lac. The first is the lac in pretty confiderable lumps, with much of the woody parts of the branches on which it is formed adhering to it. Sed lac is only the stick lac broke into small pieces, garbled, and appearing in a granulated form. Shellac is the purified lac, by a very ample procefs to be mentioned afterward. "Many vague and unauthenticated reports concerning lac have reached the public; and though amongst the multiplicity of accounts the true hiftory of this substance has been nearly hit on, little credit is given in Europe to any defcription of it hitherto publifhed. My obfervations, as far as they go, are the refult of what I have feen, from the lac on the tree, the progrefs of the infect now in my cuftody, and the information of a gentleman refiding at Goalpara on the borders of Affam, who is perfectly converfant in the method of breeding the infect, inviting it to the tree, collecting the lac from the branches, and forming it into fhell lac, in which ftate much of it is received from Aflam, and exported to Europe for various great and ufeful purposes. The tree on which this fly moft commonly gene atcs is known in Bengal by the name of the biher-tree, and is a fpecies of the rhamnus. The fly is nourished by the tree, and there depofits its eggs which nature has provided it with the means of defending from external injury by a collection of this lac, evidently ferving the twofold purpofe of a nidus and covering to the ovum and infect in its firft ftage, and food for the maggot in its more advanced state. The lac is formed into complete cells, finished with as much regularity and art as a honeycomb, but differently arranged. The flies are invited to depofit their eggs on the branches of the tree, by befmearing them with fome of the frefh lac fteeped in water, which attracts the fly, and gives a better and larger crop. "The lac is collected twice a year, in the months of February and Auguft. "I have examined the egg of the fly with a very good microfcope: it is of a very pure red, perfectly tranfparent, except in the centre, where there were evident marks of the embryo forming, and opaque ramifications paffing off from the body of it. The egg is perfectly oval, and about the fize of an ant's egg. The maggot is about the oneeight of an inch long, formed of many rings (ten or twelve) with a fmall red head; when seen with a microscope, the parts of the head were eafily diftinguifhed, with fix fmall fpecks on the breafts, fomewhat projecting, which feemed to be the incipient formation of the feet. This maggot is now in my cuftody, in the form of a nymph or chryfalis, its annular coat forming a ftrong covering, from which it should iffue forth a fly. I have never feen the fly, and cannot therefore defcribe it more fully, or determine its genus and fpecies. I am promised a drawing of the infect in its different ftages, and fhall be able foon to add to a botannical defcription of the plant a drawing of the branch, with the different parts of fructification and lac on it. The gentleman to whom I owe part of my information terms the lac the excrement of the infect. On a more minute inveftigation, however, we may not find it more fo than the wax or honey of the bee, or filk of the filk-worm. Nature has provided moft infects with the means of fecreting a fubftance which generally anfwers the twofold purpose of defending the embryo, and fupplying nourishment to the infect from the time of its animation till able to wander abroad in queft of food. The fresh lac contains within its cells, a liquid, fweetish to the tafte, and of a fine red colour, mifcible in water. The natives of Affam ufe it as a dye, and cotton dipped in this liquid makes afterwards a very good red ink. "The fimple operation of purifying lac is practifed as follows. It is broken into finall pieces, and picked from the branches and flicks, when it is put into a fort of canvas bag of about four feet long, and not above fix inches in circumference. Two of these bags are in constant ufe, and each of them held by two men. The bag is placed over a fire, and frequently turned till the lac is liquid enough to pass through its pores, when it is taken off the fire, and fqueezed by two men in different directions, dragging it along the convex part of a plantain-tree prepared for the purpofe; while this is doing, the other bag is heating, to be treated in the fame way. The mucilaginous and smooth furface of the plantain-tree feems peculiarly well adapted for preventing the adhefion of the heated lac, and giving it the form which enhances its value so much. The degree of preffure on the plantain-tree regulates the thicknefs of the fhell, and the quality of the bag determines its finenefs and tranfparency. They have learned of late, that the lac which is thicker in the fhell than it used to be, is most prized in Europe. Affam |