268 



NATURE 



\_ytily 2 2, i8So 



taken place before, and we need not again go over the 

 ground which we have aheady traversed several times in 

 these pa£;cs, when we have endeavoured to point out their 

 most probable origin and mode of propagation. 



We propose, however, in this place to devote a few 

 lines to the discussion of a cjuestion which we think has 

 not as yet received the attention it deserves, namely : 

 When is a mine in such a state that it may be termed 

 ■iiicll-vcntilatcd? and our principal reason for doing so is 

 that a statement has been already put forth to the effect 

 that the ventilation of Risca Colliery was as perfect as it 

 well could be, the total volume of air passing through it 

 being considerably over 100,000 cubic feet per minute. 



An air-current of given dimensions may be sufficient to 

 thoroughly ventilate the workings of a fiery mine at one 

 time, and it may be quite insufficient at another : for the 

 degree of sufficiency is obviously wholly dependent on the 

 amount of fire-damp given off per unit of time. Each 

 unit of volume of coal contains a certain volume of fire- 

 damp in a state of great compression — it may be in a 

 liquid or solid condition — and this gas begins to be given 

 off when the workings approach to within a certain dis- 

 tance of the space within which it is confined. The 

 greater proportion of the fire-damp is probably given off 

 immediately before the coal is laid bare, and at the 

 instant it is being detached from the face; but some 

 of it still continues in the coal long after it has left the 

 mine. 



If the workings of a fiery mine are stopped abruptly 

 and allowed to remain unworked for a considerable time, 

 we find that the amount of fire-damp given off gradually 

 decreases, until in the course of a year or so it is not more 

 than one-tenth of what it was when the mine was in full 

 work. If, on the other hand, the output of a fiery mine is 

 largely increased, we find that the workings soon lapse 

 into a dangerous condition unless the ventilation has been 

 largely in excess of its requirements in the first place. 

 The character of the ventilation is thus dependent upon 

 the output of coal for the time being as well as on the 

 amount of air. 



The daily output of Risca Colliery is stated to have been 

 1,000 tons, and supposing the amount of gas given off to 

 have been 2,SSo cubic feet per ton of coal, which is the 

 actual amount we have found by observation and calcula- 

 tion in similar mines, then we know that, if the volume of 

 the ventilating current had amounted to 30,000 cubic feet 

 per minute, the whole of it would have been explosive as 

 it returned from the workings ; if it amounted to 50,000 

 cubic feet per minute it would show a cap half an inch 

 high in the small oil-flame of a lamp, and when charged 

 with coal-dust it would form a highly explosive mixture ; 

 if it amounted to 100,000 cubic feet per minute it would 

 still show a small cap ^ to y\ inch, and it would still 

 produce an explosion when mixed with coal-dust, and 

 ignited. 



It is notorious, however, that as a rule the volume of 

 air which reaches and passes round the working faces is 

 much less than that which descends the down-cast and 

 ascends the up-cast shaft ; and when we are told that the 

 ventilation of a mine is represented by a certain number 

 of cubic feet of air per minute, we are on the safe side if 

 we estimate the useful volume to be little more than 

 two-thirds of the stated one. 



It is further notorious that the practical miner of 

 almost every grade regards a small cap on the flame of 

 the lamp, even if j to i inch high as a very trivial matter, 

 so long as he finds little or no explosive gas in the mine ; 

 and he only begins to speak of the return air as being 

 heavy or rather heavy when the size of the cap on the 

 small oil-flame reaches or exceeds a height of f of an 

 inch ; but still even in this case he is not much troubled 

 with thoughts of immediate danger. 



What then constitutes a well-ventil.ated mine ? 



We say in reply that no mine containing dry co?l-dust 



is well-ventilated when the cap on the small oil-flame of a 

 lamp is over ^ or ^-'^ inch in height, that is to say, when 

 the return air contains more than 2 per cent, of gas. 

 E\en with that amount, as we know, it will form an 

 explosive mixture with coal-dust, and we should prefer to 

 see a standard insisted upon in which not more than 

 I per cent, was allowed. 



This aspect of the question is well worthy of the 

 attention of the Royal Commissioners on Accidents in 

 Mines, and we hope they will not allow their present 

 opportunity to pass without endeavouring to arrive at 

 some definite settlement of such an important question. 



NORTH AMERICAN GEOLOGY-IDAHO AND 

 WYOMING 1 



T N spite of the revolution that was recently effected 

 ^ among the Government geological surveys of the 

 .\merican Union, provision has wisely been made for the 

 completion of the Reports of the different corps which 

 have been abolished. It is pleasant to welcome still 

 another of the stout black volumes issued annually by the 

 Geological and Geographical Sur\-ey of the Territories. 

 On the completion of the Survey of Colorado in 1876 Dr. 

 Hayden and his corps of active coadjutors moved north- 

 wards across the belt of country included in the Survey 

 of the 40th Parallel under Mr. Clarence King, with 

 the intention of mapping the territories of Idaho and 

 Wyoming to the north and west. A number of recon- 

 naissances had been made by various observers in these 

 regions since the days of Bonneville and Fremont, some 

 of the earlier work of Hayden's Survey ha\-ing been 

 accomplished there. But no general survey of the whole 

 area had been attempted, and many parts of it had never 

 been penetrated by white men. It was a vast territory, 

 including within its borders the sources of the Green, 

 Snake, and Yellowstone Rivers, and embracing the most 

 varied forms of surface and the greatest diversities of 

 geological structure. To survey this unknown domain 

 and bring its geography, geology, mineralogy, ethnology, 

 zoology, botany, and general economic capacity to the 

 knowledge of the world was the aim with which Dr. 

 Hayden and his staff started in the summer of 1877. 

 During the season the primary triangulation was extended 

 over an area of 28,000 square miles, from West Long. 107° 

 to 112° and between North Lat. 41° 10' and 43° 50', and 

 was connected with the stations made by the Survey of the 

 40th Parallel, and by the Boundary Survey of Wyoming. 

 Topographical field-work was carried on by three parties, 

 each having an area assigned to it of about 1 1,000 square 

 miles. The total area thus surveyed amounted to about 

 29,000 square miles. The geological staff was likewise 

 divided into three divisions, each being intrusted with a 

 separate district, viz., the regions of the Sweetwater, 

 Teton, and Upper Green River. 



In the report of Dr. Endlich of the Sweetwater division, 

 one of the most interesting features is his account of the 

 structure of the Wind River Mountains. This important 

 portion of the true Rocky Mountain range is formed^ of 

 three parallel chains, of which the western, and chief, 

 rises to heights of more than 13,000 feet and forms the 

 watershed of the continent. Even now its huge snow- 

 fields, which, through the clear summer air can be seen 

 gleaming from a distance of more than 100 miles, suggest 

 the presence of glaciers. When Dr. Endlich and his 

 jiarty traversed these mountains in 1S77 they found, 

 mdeed, no recognisable glacier, but abundant freshly- 

 grooved and polished rocks and moraine mounds, 

 showing the comparatively recent existence of land-ice 

 in these elevated regions. On the west side of the 



» •■ Eleventh Anuu.il Report (1877) of tlie United Sl.ites Geological and 

 Geographical Survey of the Territories, embr.acing Idaho and Wyoming. 

 (Washington: F. V. Hayden, 1879.) 



