nature of the gas obtained from the same coal varies considerably, according to the conditions under which it is obtainable. 112 lb. of common Cannel coal produce at the minimum from 350 to 360 cubic feet of carbureted hydrogen; but the same quantity of the best Newcastle coal, that is to say, such as coke readily, and send out brilliant streams of flame, which undergo a kind of semifusion when laid on the fire, produce upon an average 300 cubic feet of this gaseous fluid, besides a large portion of sulphureted hydrogen, carbonic acid, and carbonic oxide. Half a cubic foot of this gas, when fresh prepared, that is to say, holding in solution or suspension a portion of the essential oil which is generated during the production of the gas, is equal in illuminating power to from 170 to 180 grs. of tallow, which is the quantity of this material consumed in one hour by a well snuffed tallow candle six to the pound. Now 1 lb. avoirdupois is equal to 7000 grs., and consequently 1 lb. of candles of six to the pound, burning one at a time in succession, would last 70% = 40 hours. To produce the same light, we must burn one half of a cubic foot of coal gas per hour; therefore one half multiplied by 40 hours is equal to 20 cubic feet of gas in 40 hours, and consequently equal to 1 lb. of candles, six to the pound, provided they were burnt one after another. Further, 112 lb. of Cannel coal produce at the minimum 350 cubic feet of gas, and are equal to 350 divided by 20, which last is equivalent to 1 lb. of tallow, making therefore 112 lb. of coal equal to 30 17 lb. of tallow; and 112 lb. of coal divided by 17 of tallow gives six and four-tenths of coal equal to 1 lb. of tallow. 20 With regard to Newcastle coals, it may be stated that one chaldron of Wall's End coal produces in this large way upwards of 11,000 cubic feet of crude gas, which when purified diminish to nearly 10,000 cubic feet. But the quantity and quality of the gas, as stated already, is much influenced by circumstances attending the formation of it. If the tar and oil produced during the evolution of the gas in its nascent state be made to come in contact with the sides of the red-hot iron retorts; or, better, if it be made to pass through an iron cylinder or other vessel heated red-hot, a large portion of it becomes decomposed into carbureted hydrogen and olefiant gas; and thus a much greater quantity of gas is produced than would be obtained without such precautions. If the coal be distilled with a very low red heat, scarcely observable by day-light, the gas produced gives but a feeble light: if this distillatory vessel be of a dull redness, the light produced by the burning gas is more brilliant if a bright, or cherry-red, heat be employed, the gas produced burns with a brilliant white flame: and if the heat be increased so far that the retort is almost white hot, and consequently in danger of melting, the gas given out has little illuminating power, and burns with a clear bluish flame: and if this coal abounds in pyrites, a large portion of sulphured hydrogen gas is : then produced, which has the capital disadvantage of affording a suffocating odour when the gas is burnt. I need scarcely mention that it makes no difference in what form the coal is used, and that the very refuse or small coal, which passes through the screen at the pit's mouth, and which finds no market, nay, even the sweepings of the pit, which are thrown away, may be employed for the production of the gas. With regard to the pressure of the gazometer, your Correspondent is informed that experience has shown that a pressure of a column of water from an half to one inch is sufficient for regulating the proper supply of the gas to the lamps and burners; but this pressure must be constant and uniform. It is obvious that the weight of the gazometer or vessel which contains the gas is constantly increasing in proportion as it fills with gas and rises out of the water or cistern in which it is immersed; and consequently, if a constant or uniform balance weight equal only to that of the gazometer in the first moment of its immersion be employed, the gas becomes gradually more and more compressed by that part of the weight of the gazometer which is not counterpoised; therefore insurmountable difficulties would follow, because it would be impossible to regulate the size of the flames, &c. To compensate for this increasing weight of the gazometer, the chain by which this vessel is suspended, or at least such a part of it as is equal in length to the height of the gazometer (measured at right angles to the axis of the wheel over which it passes downwards) must be loaded with a weight equal to the quantity of water which the gazometer displaces; and thus the density of the gas will be uniform, or at all times the same. The diameter of the pipes which convey the gas is not taken at random, as your Correspondent imagines. Their diameters is a simple matter of calculation, depending upon the quantity of gas which they have to deliver in a given time, and the diameters of the branch pipes proceeding from them, Further information concerning the general nature of the gas light illumination, together with a description of the best machineries employed in this new branch of civil economy, your Correspondent will find in a Treatise on Gas Light, illustrated with copper plates, which will be published on the 10th of next month, by, Sir, Your most obedient humble servant, Compton street, Soho, FREDERICK ACCUM. *For this elegant contrivance we are indebted to Mr. Clegg, the engineer of the Gas Light Company. ARTICLE V. Remarks on the Older Floetz Strata of England. I HAVE long entertained a suspicion that it may be possible by comparing the organic remains found in the lime-stones, which are connected with coal-fields, with those which characterize some other rocks, to elucidate the series of secondary strata, which our island presents, and especially to determine the era of the independent coal formation. On reading Dr. Fleming's late communication on the fossils found by him in Linlithgowshire, I was so strongly confirmed in this persuasion that I have ventured to submit the following remarks on the subject to your inspection, and to that of the public if you think them worth inserting in your Journal. It seems improbable that a single species of organized beings should appear in one stratum, and then vanish entirely during an interval, and afterwards show itself again. It is contrary to what we find in nature. A fossil which abounds in one formation is often seen more scantily dispersed through a second, in a third it is scarcely found, and at length withdraws itself altogether from our view. A continual progress seems to have been made from the more simple to the more complex forms. We observe no retrograde changes. But if the extinction and revival of a single animal be thus improbable, how much more difficult is it to suppose that an entire assemblage of co-existent beings should disappear altogether, that their place should be filled during an interval by creatures of a totally different character, and that these should become extinct to make way for a reproduction of the former class? The supposition is so contrary to the usual course of our observations, that I think we may conclude, when we discover two formations to abound with similar fossils, and a third to be characterized by remains of a different description, that the two former belong to one era, and that the latter is either more ancient or more recent than both of them. If this conclusion be allowed, it will enable us to ascertain the relative age of the independent coal formation, or at least of the coal-fields in Britain. I shall first enumerate the extraneous fossils found in the oldest class of rocks which contains any, viz. those of the transition formation, and chiefly the transition lime-stone. Mr. Jameson mentions among the fossils of this rock encrinites, madreporites, tubiporites, corallites, and trochites. Von Buch found in the transition lime-stone of Norway, Sweden, and Finland, which lies under granite, a great abundance and variety of orthoceratites, some of which were many feet in length. He observes that they distinguish this formation throughout Europe. He notices also pectinites, the oniscus, trilobites, a number of large madreporites, a great many trochites, entrochites, patellæ, a few ammonites, and a great number of other univalves. Saussure found in the lower chains of the Alps, between Mont Blanc and Geneva, pectinites, terebratulites, gryphites, entrochites, a great many corallites and madreporites, turbinites, and ammonites. I shall now mention some of the fossils found in the lime-stone rocks which accompany the coal formation in Britain, and which generally shut in or inclose the coal-fields. Orthoceratites, as observed by Dr. Fleming. Their existence in the coal-field of Linlithgowshire is not a solitary fact. I have seen one which was found in St. Vincent's Rock, in the boundary of the Somersetshire coal basin. It was in the possession of Mr. Cumberland. Encrinites and trochites occur in astonishing abundance in all the rocks of this class in South Britain. Dr. Fleming has mentioned them in Linlithgowshire. A great variety of madreporites is commonly seen. Pectinites are often found in the rocks near Bristol. The trilobite is well known in the lime-stone rocks at Dudley, in Staffordshire. Ammonites occur, though more rarely, in the lime-stone of the coal formation. They are mentioned by Mr. Aikin in the coal-field of Shropshire. Terebratulites are found very commonly in all the lime-stones of the coal formation. I might enlarge this catalogue to a much greater extent; but what I have said will suffice to show that there is a general conformity between the animal remains found in the transition limestone and the lime-stones of the coal-fields. Hence it appears that at the periods when these two formations were deposited, the ocean was filled with organized beings of the same description. The astonishing abundance of these relics in the rocks of both orders testifies the vast profusion of animal life which the sea contained at each of the periods in question. That the whole of this assemblage of animals became extinct, and were afterwards produced anew, and that the ocean in the interval was filled with a different set of creatures, which suddenly vanished when their predecessors appeared for the second time, can scarcely be imagined. It follows, therefore, that the first floetz lime-stone of the Wernerian series, to which fossils of a different character are assigned, is more recent than the rocks of the independent coal formation. This conclusion is confirmed by considering the situation in which the coal basins in South Britain are found. A considerable track of country in the midland counties of England and South Wales is occupied by a red sand-stone formation, which agrees remarkably with the characters of the old red sand-stone of Werner. On this sand-stone several, if not all the coal-fields of South Britain, rest. In the neighbourhood of this tract the older formations are in many places to be seen, as in the range of the Malvern Hills, between Herefordshire and Worcestershire. Beginning from these hills, we easily trace the succession of rocks from the primitive to the newest floetz strata. I shall briefly mention the most important rocks which this series contains in this part of England. In The Malvern Hills, of which Mr. Horner has given an account, form a small range running nearly from N. to S. They consist chiefly of granite and syenite, in which no stratification can be discovered, perhaps on account of their being very much concealed by soil. On the western side of them, beds of a very hard compact lime-stone lie against the feet of the hills dipping towards the west. In conformable position with these, and frequently alternating with them, are beds of a clay rock, which varies in its appearance. some places it is a hard slate, and contains scales of mica in great abundance; in others it becomes a mere shale. These rocks contain a profusion of organic remains, particularly encrinites, madreporites, and terebratulites, Mr. Horner's account of them is minute and accurate: I only mention them for the sake of remarking their position with respect to the red sand-stone, which I have traced, and which appears to fix their place in the geological series. Mr. Horner considered these rocks as belonging to the transition formation. In this opinion he was right, if, as it appears scarcely to be doubted, the sand-stone is the old red sand-stone. As we approach these hills from Ross, we perceive that the country which lies to the S. W. of the range is occupied by a succession of low ridges lying nearly parallel to the direction of the Malvern Hills. Most of the observations which Saussure made of the calcareous chains of the Alps are here verified in miniature. The ridges generally turn their abrupt sides towards the primitive range, and slope on the other side. They consist of the lime-stone and clay rock above mentioned, the beds of which generally dip towards the W. and S. W.; but at the northern extremity of several ridges they turn round the hills, and dip northward. In the most westerly of these ridges, near Fownhope, about 13 miles in a direct line from the Malvern Hills, the clay and lime-stone rock dips at an angle of about 60° towards the S. W. Here we lose this formation. Immediately after passing over this western limit of the limestone, we find the red sand-stone above-mentioned lying upon it, and in a position exactly conformable with it. The sand-stone forms low ranges of hills parallel to the former. It dips to the S.W. at a considerable angle, which diminishes as we recede from the |