The distance from Harrisburg to Robinson's summit is 132–⅔ miles; upon the whole of this line, the only extraordinary impediments to the easy graduation of the road bed are the bridge over the Susquehanna, a deep and long cut near Newton Hamilton, and a tunnel 1,200 feet in length through a point of Tussey's mountain, and in this distance the maximum ascending gradient to Lewistown is 16 feet per mile, and descending 8 feet. Thence, to Robinson's summit, they are increased to 21 feet ascending, and 10–⅛ feet descending.
The descending gradients are generally so short that they will not be found, in practice, to decrease the load going east much below what is due to a fair working load for a locomotive on a level.
The maximum ascending gradient above Lewistown is determined by the deep cut near Newton Hamilton. The ascent of the Little Juniata seems, however, to require—to obtain an economical line—the use of this inclination, without much intermission, from Dorsey's forge to Robinson's summit. Below Lewistown the gradients are fixed to accommodate the increased trade that would fall upon the line between that place and Harrisburg, without increasing the number of trains.
These low gradients insure to us the important advantages of a single pair of drivers for the passenger engines, upon the eastern division, and, with these rates of inclination, we are enabled to make the line conform to the natural features of the country (above high water mark) without decreasing the curvature below 955 feet radius, except at the east end of the Susquehanna bridge, where a radius of 880 feet has been admitted.
All of our efforts to save distance, by deviating, temporarily, from the immediate valley of the river, involved either the use of high gradients, not justified by the distance saved, or an increased cost that was equally unwarranted. The beautiful valley of the Kishacoquillas offered the greatest temptation to leave the river route; but here we would have had to encounter gradients, in both directions, of 26–4/10 feet per mile, a bridge over Mill creek, 1,200 feet long, 111 high; another over a small tributary of the Juniata, 850 feet long and 150 feet in height, together with several others, or embankments of great magnitude, across ravines in the north slope of the river hills. These difficulties, added to 342 feet of additional elevation to be surmounted at the Allentown summit, so greatly overbalanced the small increase of curvature and distance (7/10 of a mile), by the river route, that it could not be adopted. It was also ascertained that by the use of the maximum gradients required on the valley route, the shortest line could have been procured by the river, and at the least cost. A fact, conclusive in itself, as to the proper route.
I deemed it unnecessary to make further instrumental examinations of the Stone mountain route, feeling satisfied that even if a line could be obtained in that direction which would approximate to an equality, in an engineering point of view, with the route selected—which, from a reconnoissance of a portion of the line and an examination of the plots of Mr. Schlatter's surveys, I should consider quite improbable—that its additional cost would entrench so much upon the means of the Company as to place it entirely out of the question.
A line was traced from Huntingdon to the Frankstown branch of the Juniata, below Williamsburg, across Tussey's mountain, by which a saving of distance could have been made nearly equal to the Stone mountain route, but its high gradients, cost, and the length of time that it would require to build the road over it rendered it equally objectionable. The valley of the Frankstown branch was also surveyed; the route by it joining the Little Juniata line at Robinson's ridge, but it proved both longer and more expensive than the latter. The searching examinations made of the whole region offering any chance for a more practicable route, on the north or south of the Juniata, leaves no doubt upon my mind but that the best line has been procured for the eastern division. Its comparatively easy curvature and low gradients, adapted in their inclination to the direction of the largest business, and extending from the eastern terminus of our Road to the foot of the great barrier that divides us from the west, give it advantages that are not equaled by any other route proposed, between the east and west, and can not be too highly appreciated by the Company.
Before determining the point to pass the mountain, a full examination of its crest was made, from Cedar Swamp summit on the south, to Three Springs Gap at the head of Moshannon creek on the north, embracing a distance of 44 miles. The following table will show the elevation, above tide, of each summit within that distance; also, that at Emigh's Gap, on the northern route, and at the head waters of Castleman's river on the southern:
Tabular Statement of Depressions of Allegheny Mountain.
| Name. | Waters Divided. | Authority. | Feet above Sugar Run Gap. | Feet below Sugar Run Gap. | Feet above Tide. | |
| Summit of Chesa. & Ohio Canal | Castleman's and Potomac | U. S. Engineers | 476 | 2739 | ||
| Albright's Summit | do. do. | 141 | 2424 | |||
| Sand Patch | do. | do. do. | J. Knight | 129 | 2412 | |
| Chambersburg and Pittsburg Survey | H. Hage | 264 | 2547 | |||
| Cedar Swamp Gap | Raystown Branch of Juniata and S. Fork of Conemaugh | S. H. Long | 160 | 2443 | ||
| Bob's Creek | do. | Raystown B. and Conemaugh | do. | 213 | 2496 | |
| Big Spring | do. | Juniata and Conemaugh | do. | 314 | 2597 | |
| Laurel | do. | do. do. | do. | 222 | 2505 | |
| Adams | do. | do. do. | do. | 175 | 2458 | |
| Portage and Summit | Juniata and Clearfield | C. L. Schlatter | 41 | 2324 | ||
| Sugar Run Gap | S. H. Long | 0 | 2283 | |||
| Burgoon's | do. | do. do. | C. L. Schlatter | 80 | 2363 | |
| Kittanning | do. |
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