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It till to the lot of the writer to sjiciid the wiiitvr of ISSo-fi at the .summit of tiic .Selkirk .Moiiiitiiiiis, iiir the imrpose of observiiij; .snow wlichw, witli ii view to the ijroper protociion of tlie t^aiiadiaii Pacific Railway from their ettecis. The iollowiiiii jiapi r emhodies a lew fiicts that may prove of j^ciural interest to the Eni;iiieeriii<5 profession. I'lie Selkirk .Moi"itains lorm a chain lyiiij; to the we.st of the Ifocky Alountains. They ;-. divided I'hpui them by the Columbia Valley, runninu' apjiroximately uortl. and south, ancends the eastern slo, e of the .Sel- kirks from the( olumbia Valley by the Valley of the Heaver and Bear Cneks, tiilldwiiiii the valky i^f the former fir-t for aliout 14 miles, and the latter lor ti miles. 'I'he altitude ascended in this distance is 2,200 teet, and as the valley of the Hear Creek falls very rapidly in the last •f miles of it> descent from the summit, the railway, in onler to make the ascent on jiracticable grades, has 10 leave the bottom of the beaver ValUy some (J miles from its point of departure from the Columbia Valhy, and climb up on the mountain side foUowiiij!, the contour of the slope. I'he eft'ect of this is to throw the line high up above the valley- bottom- — at some poiiUs as unieli aseight or nine hundred feet— and to give dee)) crossing's of the ravines or gullies above spoken of, by which the mountain side is fissured. 8ome of these bridge crossings are 150 feet deep, while one— that of Stoney Crcjk — is 28(i feet deep, unikiug, probably, the highest wooden bridge on the American Continent. The desceut of the V\^estern slope is made l)y the valley of the Illc-cillc-waitc River following what has been named " Roger's Pass ' mit nf compli- ment to the Engiueor who recommencU'd the adoption of this route to the company. Here, as on the eastern slope, the d<'seent of the valley is at first so rapid that it is impossible for the railway to follow the valley bottom. Ihit the difficulty has been cleverly got over, and the ro(|nisit(! fallobtiiiiu'd im a pruoticablc j;!-!!!!!', hy iiimiiiiu tlu' line ii|> a tributary valley and dduliliiiji liai'k upon it.sclf' in tlir lorni of a lii(i|). JJy tliin jilan tlic line 1, ..* bciii broujilit down to the bottom of tlio valley, nttlieeoj^t of nime three miles additional len>:th, and the necessity tor C(intinuin); it liij^li up iiionji the mountain nide has b('eii obviated. 'I'he Selkirk cliniri fornix, a>* it were, a lofty wall runninj; north and south, lieinj; very nniel; liiulur tlian the mountain.^* to the west, it ix the first and oliief barrier that the moisture laden currents of air from thu Pacifie ( k'eaii eneounter on their eastward passafje. This warm air is int<'reeiited and the moisture condensed by contact with the cola Selkirks, entailiii;.' la'avy rain in summer and deeji snow in winter; and it is inter- estiiii; to note that the snow fall on the western -lope of the Selkirks (beiiif; the jilaee when the firstcunlact with the warm air takes places) is much heavier tlian on tht' eastern sIojk'; while the aviraiie fall on the Selkirk rani;e nmeh exceeds that on the Rocky .Mimnliiiiis. The i:r( ater the ditl'erinee in temjierature, the larger will he the condensation taking place, and consccjuuitly the heavier the fall of rain or snow. Thus in cold winters the snow may be expected to be deeper than in mild. This conclusion is vcrifiid by obf-crvation. The winter of 1884-5 was cx- trtuiely cold the thernionicter during the latter part of December mark- ing, fiir some days, many degrees bilow zero, and reaching, on the 24th of thatmontli, a miniumm of— 42 '^ , and this was succeeded by a .Janu- ary (if great cold during the first half The .snow fall during that winter at the Selkirk Summit was very large, agjjregatiiig more than 30 feet in dcptli, wliile during ten consi cutive days there was a fall of no loi-B than nine feet. The winter of 188r)(! was much milder, and the t:tal snow tall 15 ft !) ins. The uit an temperature for the month of 1 )eceniber was -I- 21f =■ , and the lowest — 1 = ; the snow fall during tlic same period was only 3 ft. 4i ins. In January the mean temperature was + 2 = , and the minimum — 30 - , while the snow fall was 7 ft. 2 ins. The greatest snow fall in any 24 hours occurred between a.m. of the 23rd and a.m. of the 24th, when 17^ inches fell with a mean temperature of --8°. From a.m. of the 23rd to a.m. of the 27th, 4(1^ inches fell, whih the mean temperatuie was ( = , and tJiis was much the heaviest snow tail cxpcnenced in any ibur consecutive days. 'JTie lowest temperature occurred on the night of the 21st, when — 30= was recorded ; and it is significant that the ])eriod of lowest temperature immediately pre- ceded that of greatest snow fall. February was a mild month; the mean U-mperature was + 27 "=, the minimum — 2 = (on the last day of the month), and the snow fall 2'. 3|". But tluiugh a high temperature causes a diminution of the snow fall, it is always accompanied by more wind tlian prevails with a low ther- mometer. Though there were no in,strumciits tor measuring wind velo. cities and pressures, still personal observation testified that during the mild winter of 1885-t; there were more ireijuent and uuue violent gales than during the cold winter of 1884-5. Often, too, while it was ([uite calm in the valleys, the gale could bt heard roaring in the mountain tops. The effect of these fre(|Ueiit giiles is lo brush the snow off the exposed and prominent parts, and to lieap it into the pockets and basins of the mountain side. These form the gathering places for the aval- anches, or snow slides, which occur at intervals throughout the winter- and it can easily be understood how the masses of snow, thus packed in by the wind, increase until they lose their balance, as it were, and toppling over, or sliding out, ru,sh down tlie mountain side, with accele- rating velocity. As a matter of direct observation, slides are most frequent and largest during or immediately after very violent wind, when the thermometer is standing high. But from the preceding argument it seems probable that the wind, as the indirect agent, has more to ilo with the slide than the rise in the thermometer. There is never viole-it wind with a very low theiinimK ler. and slides seldom occur at such tiuiperature. Thus, though the show tall is the prime cause of the slide, and the ileeper tin' snow the greater the slide as a rule, yet we see that in a mild wintt r. with moderate fall, the more fretjuent and violent wii'ds, ,is comjiared with a cold winter, tend to compensate for the reduced snow i'all. by drifting the •■ pockets "to overflowing, and thus to maintain the avalanches at something like a constant i|uantity. The slides of the winter ol' lHS5_(i were certainly less in bulk than those of 1884-5, hut there was no such difference as would be inferred from a direct comparison of the ns]iective snow- fnlls ; and in some places slides, occurnxl In the inriiier y( ar where there were none the year befi re. But though it is true that year by year tlie slides maybe looked for to much the same amount, there are uumiHtiikablc evidences, in the rxi.ni hikI Idif^di „f did slidi. triickH, jiiirtially wivintl with tiuiijcr of smiit' joais' growth, that tlicro arc (iccasioiial wiiitci> wh' i. txii|ptioiial coiidilioiis jircvail, niul wlicn the slides dcscwid in Mtupiiidouh viduuif. Thi'ii' arc two cla>wc of .-lidcM ; what riuiy he called the " heiicli slide "and the " gully i-lidc.' The gully .>.nic.« from a narrow and deepeleft in the mountain side, which exUiids upward;* for perhaps one or two thousand feet. At the lop of thi,« clcfi there is ]irnbablv a dec]) jiocket oi basin in which the miow galla is. At the mouth, which is tonic 800 to 1,500 feet above the valley, the -rrcai heapof debris— the accnniulatiun of nmny ye irs— eouinienccs. It spreads out hm-like, and its width at the valley bottom may often nie:isiirc over \,2 d feet. Winter after winter. :ind ui.iny times during the same winter, the slide rushe.s down the gully and shoots out upon tlic debris Imap— the tc.s ol rock in its course TIk'SC gully slides do n.it bring down large c|uantities of snow on c;ich oce.ision, ten or twelve thousand cubic yards is about a maximum. The tirstslide probably follows the centre line down the mlus, le.iving in its course small heaps of bard packed snow. The second encounter- ing thcs(! obstructions, deflects to the right or left, tbllowiiig tiic line of le;ist resistance ; the third behaves in like manner; .md so on, .so that by sfiring the wlude ol the ■• fan " has been pas.sed over, and the snow heaped uji .ilong its base. The sl<.| . of these d.bris heajis varies IVoui U t« 1 to 3 or 4 to 1, according as room is ahordcd in ihc valley for them to spread. The velocity of the slide depends upon the angle of the .sKjpe, the height from which it comes, and the condition of the snow. During early winter when the snow is light and powdery, and lying in this condition to a considerable depth, the slidi is impeded by gathering snow as it descends, and the velocity is not very great, probably not exceeding 30 miles an hour. But later, w hen the .slide-tiack has been worn smooth by fre(|uent avalanches, the slide sometimes descends with terrific velo- city. Observation and the careful weighitig of various considerations induce one to rate this velocity as high as 10(1 to 120 mihw per hour A measure is obtained from the velocity of the wind generated by the slide. It will readily b-' granted th;it a mass of some ten or twenty thousand cubic yard^ descending rapidly, will of necessity cau.se a strong current of air, while at the same time the velocity of the current will not be greater than thai of the ma.ss generating it. On either side of one of the.sc last snow slide track.s. at the bottom of the slide, may sometimes be seen the evidences of great wind force. Healthy trees, from a liiot to two feet in diameter, are broken, leaving shattered stems 15 to 20 feet in beigjit, .split and torn as if .>truck by lightning. Sometimes the wind continues beyond the slide, tearing for itself a track through the standing timber, nud leav.ng a sharply defined lane in its rear. 'I'lie velocity id wind iu|uired to do such work must be very great. The writer has jicrsonally noticed the action on standing timber, of a gale having a ncordcd velocity id' 08 niihs ]iei hour (in Scotland, I'Vbiuary. 18Hlj, and llir than that aci|uircd by a snow slide on a similar .slope, but still tills experiment goes to .sjiew that the vilocity (d' a slide may be even considerably greater tli:m that assumed. The writer had ojily one op- ]Mirtuiiity of personally noting the time of descent of a fast slide. This was one which occurred on the oth of February. The time of descent, after i.ssuing l'i(mi the month id' the ,gully, about SOO feet abc.-ethe valloy, WHS somi'wlint U'sh tliivu '20 sccoiiJh ; tho rato of final velocity Wdiilil. therct'orc, lie soiin'tliiiij,' ovir 50 iiiilutiper hour, without ftllowiiif: lui- the initial vi Idcity tlu' sliiK- nia> 'lavc Imd on leaving' tho f,'ully. The slide tr.iek was not i^tci ji, auil tliiri- wm- im wind iffeetH [iripduced in staudiuj! limber nt tli.' foot of thu slide. It in only from copwiderationH Huoh an the forc>;oin^ that any cMtiinate of the velocity of -lid.s lia-i been arrived at. It is seldom that oik; happens to be sufficiently near to a slide at the tinicof it« occurrence, or ill a sufficiently wife po.sitinn, m observe its time. But thouj^h there is (■vidence to show thai very liiuh velocities are sometimes attained, yet it seems probable thai siieh is nut fre((ueiitly the case. The other form of avalanche occurs when the snow irathers upon a wide. ' bench," situateil perhaps two or three thousand feet above the valley. When the aecumulaU'd snow becoim's too ureat to hold its position longer, it slips over the edge, and rushes down the mountain sidi!, on a track from a thousand to fifteen hundred feet in width. The (luantity of snow broui.'ht down in this manner is very much greater than tlint by the gully slides, and though the velocity is usually less the ofFccts are more overwhelming. In one such .slide, covering a track 1100 feet wide, the (|uantity brought down roughly measured L'50,OoO cubic yards, and in former years the (|Ua'itity has been far in excess of that. 'I'he.se bench slides do not come fr'utly during the same win- ter, as do the gully slides. It seems as though the whole winter's ac- oumulatiou were carried off in one effort, and not brought away piece meal as in the other case. The weight of hard packed .snow eumposing a slide varies from 25 to 38 lbs. pi'r euliic foot, according to the state of the atmosphere and the amount of pre.-sure to which it has been subjected in coming down. In sjiring, wliel wet snow rolls down in large balls, the weight is greater than in nudwiiit"r; but some .slides that had come down in midwinter, when the ■now was perfectly dry, weighed ;{4 and 35 lbs. per cubic foot. Tlii- greater the velocity of a slide, the heavier the snow eomiiosiiii; it becomes, owing to its being more compacted than when tlie slide travels slower. 'J"he time of year when slides are largest and most frequent is from the middle of January to the latter part of February. These are •' win- ter slides." formed of large masses of (juito dry snow. In 3Iareli and April there are numerous 'sun slides," caused by the melting of the snow and iee, but these are not of any importance as companil with the others. In erecting structures for the protection of the line of Railway, the governinu priiiciiile is that they should offer no resistance to tfe slide. The force generated by the rapid descent of mas.ses so large and heavy, is such that no structure that could be built would withstand it. Where the line runs along, and is " iieiiched " into the mountain side, in the manner that has been described, the sled is constructed so as to eon- tiiiue the slope of the mountain, and shoot the slide across the track into the valley below; and the miUH' nearly the .-lopt' ot the shed roof coincides with that of the mountain side, the less will be the shock it receives from the passage of the snow. Where the line runs along the valley bott(nii. and slides descend from either side, strong cribs are built iiarallel to the track, with rooting between, while the backs are tilled in with earth at a gentle slope, that allows the .slide to rise up and pass over the line. By carefully observing the action of slides, and erectiii"' >lieds at all places where rei|uired, the line eaii be so protected as to run trains in safely, and wiili regularity, throughout the winter, no matter how great the avalanches may be. Though the Company has not >ueeeeded in doing tlii-- tlioronghly during the past winter, yet this failure has arisen rather from the imjxissibility of erecting all the requisite shed^ during the >hort preceding season, than from inability to cope with these great forces iif nature.