The Railway Library, 1909. VariousЧитать онлайн книгу.
It will be perceived that the lowest point in the mountain, except at Emigh's, is Maple Gap, from which issues Bell's Run (a branch of the Little Juniata), on the east, and Sandy Run of Clearfield, on the west. This point is 61 feet below Sugar Run Gap and could be further reduced 150 feet by a tunnel 700 yards in length. If the ground had been favorable beyond the summit, this route would probably have offered the greatest advantages to cross the mountain, but it opens westwardly upon the deep valley of Clearfield, a descent into which would involve the necessity of a resort to as steep a gradient on the west side of the mountain as that required on the east; and the elevation thus lost would have to be regained by following up the valley to Laurel Swamp or Munster summits, in the ridge that separates Clearfield from the Conemaugh, which is here the true backbone of the country.
Any attempt to carry a line along the west slope of the mountain, to avoid the descent to Clearfield, would, from the rugged character of the ground, prove impracticable, without a vast increase in its cost, length and curvature. No other point offers equal advantages to cross the mountain until we reach Sugar Run Gap, which is 41 feet below the Portage Railroad summit, and may be reduced 120 feet more by a tunnel 2,000 feet in length. Emigh's Gap, which is still lower than Maple Gap, could not, on account of its gradual slope, be reduced by a tunnel of moderate cost, and it is also too far north for a direct route to Pittsburg. South of the Portage the Alleghenies become the watershed of the Union, dividing the streams that flow into the gulf from those that empty into the Atlantic. They here assume a more elevated character than while separating only the tributaries of the Susquehanna, affording no opportunity to pass them by a line adapted to locomotive power—unless by a tunnel of immense extent—until we reach Bob's Creek Gap. The accompanying profile, which exhibits the crest line of the mountain (for 44 miles) will give a more definite idea of the relative height of these summits.
The mountain on each side of Bob's Creek Gap rises to a considerable height, making it appear, to a casual observer, a very deep depression; and, from this circumstance, it has generally been considered by the residents of the adjoining country to be the lowest pass in the Alleghenies, and, as it falls off rapidly on either side, it has also been supposed that it could be farther reduced by a tunnel of moderate extent. The several surveys of the mountain, however, prove it to be 212 feet higher than Sugar Run Gap, and, to reduce it to a level with the surface of the ground at the latter point, which is 120 feet above the grade of the adopted line, it would require a tunnel 1¼ miles in length, to be constructed under very disadvantageous local circumstances.
Cedar Swamp Gap, still farther south, is 53 feet lower than Bob's Creek Gap, but it falls off on each side so gradually that it could not be reduced conveniently more than 40 feet.
Neither of these points, therefore, which are the only passes worthy of notice south of the Portage Railroad that lie within the region over which a direct line to Pittsburg must necessarily traverse, afford depressions that will compare favorably with those farther north; nor does the ground leading to them, east or west of the mountains, offer equal facilities to obtain a line of uniform ascent to the summit. The distance from the Conemaugh is too short to overcome the elevation with the gradient used on the western division, and, from the Juniata, the greater height to be ascended would continue the line so long upon the mountain steeps that it would be exceedingly expensive to procure a roadbed with a gradient even higher than 80 feet per mile.
From the foregoing description of the most favorable mountain passes, it will be seen that Sugar Run Gap offers the greatest facilities to cross the Allegheny.
It now becomes necessary to consider in what direction the Road can be carried thence to Pittsburg. From an inspection of a map of the State it will be seen that a straight line, drawn from this gap to Pittsburg, will fall on Munster, Beulah, and follow the valley of Black Lick for nearly its whole extent, and intersect the Conemaugh near Blairsville; thence it crosses the country lying within the elbow formed by the Kiskeminetas and Allegheny rivers, passing the Loyalhanna and Crabtree waters, and following, generally, the high and broken ridge parting the Allegheny and Monongahela rivers. That line, which would approximate most nearly to this course, would—all other things being equal—be the most desirable for the Road.
The operations of the different corps, on this division, have been confined to surveys that were necessary to determine the point of crossing the mountain and to the regions between the Conemaugh and Pittsburg, west of the Chestnut ridge. Our examinations have not yet been sufficiently extensive to enable me to give a full description of that part of the country between the mountain and Blairsville, and I shall therefore leave it for a future report, with the simple remark that, from the information before me, I am satisfied that a practicable line may be obtained by the valleys, either of the Black Lick or Conemaugh, within the maximum gradient used upon the western division.
The district of country over which it will be necessary to carry the road from the Conemaugh to Pittsburg is one of remarkable intricacy. It lies wholly within the coal measures, and has, at some period, evidently been nearly a level plane of vast extent, covered by the ocean. The discharge of the waters from this wide spread field seems to have been sudden, forming numerous circuitous channels in every direction, cutting deeply into the soft horizontal strata of this region, in their descent to the tributaries of the Ohio, leaving the intervening ridges washed into so uneven a surface as to render the passage of a railroad along them entirely out of the question. A line following the Conemaugh—which bears northwest from Blairsville—to the Allegheny would avoid this difficult country, but the length of the route would be increased fully 50 per cent., and it is, therefore, inadmissible.
A route with higher gradients than those adopted on the Juniata throughout this division seems to be called for by the topography of the country.
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