and a great altitude. The two things seem incongruous. But yet, in Colorado they are co-existent. The Geological age of the Colorado coals has been a puzzle to men of science. It is now the general opinion that none of them belong to the true Carboniferous series, but that they are Tertiary or Cretaceous formations differing greatly in age, though not in any case reaching back to the Carboniferous era. They differ much in quality-in fact, all grades are represented.

Along the eastern mountain-base, north and south of Denver, the light Tertiary lignitic coals are found, and, although friable, high in water, and therefore not of great caloric power, these coals are mined extensively and sold as cheap fuel. They lie at an elevation of from 6000 to 7000 feet above the sea, and the seams which are being worked reach from ten to twelve feet in thickness. About 150 miles south of Denver, much older coal-measures (undoubtedly Cretaceous) are encountered. These measures yield strong bituminous coals. At El Moro and around Trinidad in the Raton Mountains, seams 11 ft. in thickness are worked, and the coal is not only a strong fuel, but produces an excellent coke, which is used extensively in the manufacture of iron and steel, and in silver-lead smelting. Other coals of the same series are semi-bituminous; they will not coke, but are better steam coals, and are preferred for reverberatory furnaces. Some 3000 to 4000 tons daily are produced from this locality and the neighbouring mines near Walsenburg. A large area of the Trinidad coal-field is covered with a thick overflow of basalt, and many trap-dykes cut through the coal-measures. Close to the dykes the coal in places has been converted into a porous natural coke, hardly distinguishable from the coke of commerce.

The

Up amongst the mountains still purer coals are found. Crested Butte, situated in about the centre of the western half of the State, is a great coal district. Here coking coal of a very fine quality and of the same geological age is mined, and the coke made from it is excellent. mines here are some 9000 feet above the sea-level, and are surrounded by an amphitheatre of lofty mountains. As these pure and very bituminous coal-measures approach the actual mountains themselves, which are mostly composed of igneous rocks, they rapidly change in character; they become less bituminous, then semi-anthracitic, until within a certain limited distance from the trachytic rocks, perfect anthracite, containing from 89 to 92 per cent. of fixed carbon, is encountered. Nowhere is this change better exemplified than along the valley for a few miles north of Crested Butte. On the left side the coalmeasures are exposed. At Crested Butte they are strongly bituminous, and the little town is all aglow with coke-ovens every night. Two miles above, these same coal-seams are found to be worthless, having undergone partial conversion into anthracite, but being, so to speak, neither one thing nor the other. Still farther up the valley, some four miles from the town, and at an elevation of about 1200 feet above it, the coal is completely converted into anthracite, and extensively mined, the anthracite being of excellent quality. From this source all Colorado and the whole country westward to San Francisco are supplied with this highlyprized fuel. The anthracitic area at this place is very limited.

The

coal-seams run through a level isolated plateau on the east side of the valley, some 200 feet below the top, and some 800 feet above the base of this plateau, which occupies little more than a square mile of surface. Around the plateau, which represents the original formations in statu quo, the coal-measures are carried away by erosion or crushed to pieces by the mountain upheavals. Other areas, adjacent to the igneous rocks, which have escaped erosion, also contain anthracite, in different parts of this extensive coal-field. These, however, are not yet available, because they have not yet been tapped by a railway. The railway supplying these Crested Butte coal-mines carries out an average of about 1000 tons of coal and coke daily. There are many silver-mines in close proximity to these coal-mines, and auriferous gravels are worked along many of the streams.

Some fifty miles north-west of Crested Butte, another portion of this coal-field is actively mined, viz., between Glenwood Springs and Aspen, where coke is also made. Aspen is a great silver-mining centre, where millions of dollars of silver and gold are produced annually.

There is one other coal-mining centre worthy of mention. This is at Durango, far away in the south-west corner of the State. Here there are two series of coal-measures. The more recent, geologically, is of great thickness. In about 120 feet, measured at right angles to the strata, there are ninety feet of coal, the intervening layers being shales and sand-stones. One of these individual seams is fourteen feet in thickness. This coal cokes well, and stands the weather well, but is too high in ash to rank with the best coals of the State. The older coalmeasures are numerous, but they seldom exceed four feet in thickness. One of these seams is worked. The coal is a coking coal of very high grade. It furnishes coke for the smelting-works at Durango, and fuel for the mines of Red Mountain, Silverton, Telluride, and Rico. All these flourishing and productive mining-towns, which together furnish 2 P

VOL. VII.

from three to four million dollars a year, in silver and gold, lie within a radius of fifty miles of the coal-mines. There is a great future for this south-western corner of the State. It has wide-spread mineral wealth, vast coal deposits of high quality, and a very fertile soil, with broad valleys and abundance of water for irrigation; also a splendid climate. Hitherto it has been so far away that it is only now attracting attention. It is now well opened up by railways, which are doing a good business.

In referring to the gold and silver mines of Colorado, I will confine my remarks chiefly to pointing out the different conditions under which the precious metals occur in various places throughout the State. These metals occur for the most part under conditions which may be classed under three tolerably distinct heads:-(1st) In true fissure veins, where the matrix filling up the cleft or fissure is mostly quartz, but may be represented by a great variety of non-metallic substances in whole or in part, such as Sulphate of Baryta (heavy spar), Fluoride of Calcium (fluor spar), Lime Spar, or crystallised carbonate of lime. The mineral is deposited unequally through the matrix either from solutions or perhaps in a gaseous condition accompanied with super-heated steam. The true fissure, however, which may cleave its way through any number of different strata at any angle, is here the governing feature. (2nd) These metals are found deposited between previously existing strata, generally sedimentary, sometimes sedimentary on one side and igneous on the other. Such deposits are known in Colorado as contact veins." There are generally evidences in these cases of movement or slipping having taken place, thus allowing water to percolate between the strata where the contact veins occur. One stratum is generally magnesian limestone, which is easily attacked by water more or less impregnated with various salts, amongst them, salts of the precious metals, especially associated with salts of lead, copper, and iron. The other stratum on the other side of the "contact vein" may be anything-very commonly it is porphyry. (3d) We find the precious metals and their salts, deposited during the last stages of solfataric action, in places where thermal springs, mud-volcanoes and the like have formerly existed, often associated with dykes of porphyritic rock. Subsequently the tubes or channels of the springs are filled with saline and other deposits containing the metals in combination, which also often impregnate the contiguous country rock, producing large irregular masses commonly spoken of as ore bodies.

Now, the first discoveries of precious metals made in Colorado were those of free gold in the beds of certain streams in the mountains immediately west of Denver, and in gravels at the heads of the Arkansas River, in the neighbourhood of what is now Leadville. Then true fissure veins were discovered containing gold and silver, but mostly silver, and, the true fissure vein being a well-recognised feature, the mining laws of the United States were framed to meet the requirements of alluvial gold deposits and true fissure veins. The discoverer of a vein was allowed to claim 1500 ft. in length along the vein, and a surface area of 300 ft. in width, and he might follow the vein in depth to any distance beyond his side-lines-in fact, wherever it might dip within the 1500 ft. of length.

When, years afterwards, the now famous Leadville mines were discovered and opened up, most of them bore no similarity to true fissure veins, but a great similarity to a coal-seam. They were mostly "contact veins or deposits of metalliferous material along the line of contact of two dissimilar strata, and the then-existing mining laws did not strictly apply. An appalling amount of litigation was the result. To allow a discoverer to follow a contact vein which occupied the interstices between two horizontal strata, indefinitely beyond his side-lines, was giving him an enormous latitude-far more than was intended by the fissure-vein laws, or contemplated by their framers. Both judges and juries were at their wits' end, and the jurors had to be invoked to frame new laws and modify old ones. Gradually matters settled down, partly as the result of compromises amongst the contestants, and partly as the result of the decisions of the Courts. After Leadville came the Aspen discoveries, and although the metalliferous material was here again mostly found in "contact veins," large masses or bodies of ore were unearthed which had neither distinct walls nor definable direction nor apex, nor any apparent fixed boundaries, so that the Courts were again crowded with litigants. The general tendency of all this recent litigation has, however, been to restrict the limits of each mining claim not only to its end-lines, but also to its side-lines produced vertically downwards. In other words, to restrict a claim, unless it be undoubtedly a true fissure-vein, to 1500 ft. by 300 ft. in vertical depth as well as at the surface. To pursue this subject further in a short paper like this is impracticable. My object is chiefly to point out how many difficulties of an unlooked-for and unavoidable character have attended the pursuit of gold and silver mining in Colorado, and to show also how old theories and experiences have to be modified by the results of time and a wider knowledge.

Throughout Colorado electricity is much used not only for lighting, but for motive-power. Amongst the mines advantage has been taken of the water-power furnished by mountain-torrents, and by means of a system of hydraulics very similar to that used in hydraulic gold mining, small columns of water with from 300 to 600 feet of head or pressure are made to turn wheels of peculiar construction which, in turn, work the dynamos. In this way electricity is cheaply generated, and is sold to the mining companies at about 2s. daily per horse-power for working hoisters, drills, tram-roads, in some instances coal-cutting machines, as well as concentrating mills and other appliances.

Great success has accompanied the effort to bore for artesian water all over the State. In and around Denver there are hundreds of artesian wells in use. The domestic water-supply of the town of Alamosa is furnished from artesian wells. Throughout the western half of the Great San Luis valley nearly every farm has its flowing well, artesian water being generally reached in this locality within 100 feet of the surface. In fact it is the exception not to strike artesian water in any valley where it is bored for; and in almost every district boring machinery can be obtained.

THE BRITISH ASSOCIATION, 1891.

Proceedings of the Geographical Section.

THE sixty-first Annual Meeting of the British Association for the Advancement of Science took place at Cardiff, commencing on Wednesday, 19th August. Dr. William Huggins was elected President.

The number of tickets issued was 1488, realising a sum of £1664. Grants of money for scientific purposes were made to the amount of £1013, 15s. 6d. Out of this sum the Geographical Section obtained £75 for the purpose of instituting a series of systematic observations on the climatological and meteorological conditions of Tropical Africa. Other grants, more or less subservient to Geographical investigation, were made as follows:-Meteorological observations on Ben Nevis, £50; seismological phenomena of Japan, £10; photographs of meteorological phenomena, £15; photographs of geological interest, £20; underground waters, £10; fauna of Sandwich Islands (renewed), £100; zoology and botany of the West India Islands, £100; prehistoric remains in Mashona-land, £50; North-western tribes of Canada, £100; and habits, customs, etc., of natives of India, £10.

The Geographical Section had this year as President a scientific geographer of high repute. Mr. Ravenstein's presidential address, which we publish as an Appendix, was a masterly survey of the progress of cartography; and, incidentally, it contained some notable remarks on the field of Geography. The office-bearers of Section E (Geography) were as follows:

President.-E. G. Ravenstein, F.R.G.S., F.S.S., F.R.S.G.S.

Vice-Presidents.-Colonel Sir Francis de Winton, R.A., K.C.M.G., C.B.; H. Seebohm, HON. SEC. R. G.S., F.L.S., F.Z.S.

Secretaries.-John Coles, F.R.A.S., F.R.G.S.; J. Scott Keltie, F.R.G.S. (Recorder) ; H. J. Mackinder, M.A., F.R.G.S; A. Silva White, F.R.S.E., SEC.R.SCOT.G.S.; Dr. Yeats.

Committee.-Right Hon. Lord Aberdare, G.C.B., F.R.S.; Professor Copeland; Professor Boyd Dawkins, F.R.S.; Dr. R. W. Felkin, F.R.S.E.; Dr. Hugh R. Mill, F.R.S.E.; E. Delmar Morgan; Principal Grant Ogilvie, F. R.S.E.; Colonel T. H. Holdich, R.E.; Dr. J. S. Phené; Trelawney Saunders; G. E. T. Smithson, SEC.T.G.S.; Eli Sowerbutts, SEC.M.G.S.; G. J. Symons, F.R.S.; Colonel H. Tanner; J. Thomson; C. T. Whitmell; Lewis Williams, J.P.

The following is a list of the Papers read in Section E (Geography):

1. President's Address.

Thursday, 20th August.

2. John Coles, F.R.G.S.-The Art of Observing.

3. J. Scott Keltie, F.R.G.S.-Geographical Education.

4. Miller Christy.-Trees and Plains.

5. Dr. Hugh R. Mill, F.R.S.E.—The Homology of Continents.

6. A. Silva White, F.R.S.E.-On the Comparative Value of African Lands.