From the portals and from the bottoms of the shafts the headings are driven. If the tunnel is to accommodate no more than a single track it will be built from 15 to 16-1/2 feet wide, and from 21 to 22 feet high, inside of its lining; so the general method is first to drive a top heading of about 10 feet in height up under the roof of the bore. The rest of the material is taken out in its own good season on two following benches or levels. Piercing a granite mountain is no rapid work. When the Pennsylvania Railroad built its second Gallitzin Tunnel in 1903, 13 men, working 4 drills in the top heading, were able to drill 16 holes, each 10 feet deep, in a single day. The engineers there figured that each blast removed twenty-three cubic yards of the rock. At night, when the "hard-rock men" were sleeping and their drills silent, a gang of fourteen "muckers" removed the loosened material. Slow work that. The Northern Pacific finding its way through the crest of the Cascade Mountains by means of the great Stampede Tunnel, nearly two miles in length, demanded that the contractor work under pressure and make 13-1/2 feet of tunnel a day. The contractor, working under the bonus plan, did better. With his army of 350 "hard-rock men," "muckers," and their helpers, and his tireless battery of 36 drills he sometimes made as high as eighteen feet a day from the two headings. On a three-year job he beat his contract time by seven days. The Northern Pacific paid the price, $118 for each lineal foot of tunnel. That was a high price, occasioned largely by the fact that the work was carried forward in what was then an almost unbroken wilderness. The Wabash finding its way through the great and forbidding hills of Western Pennsylvania to Pittsburgh a dozen years later was able to dig its succession of tunnels at an average cost of $4,509 for 100 feet. Of that amount $2,527 went for labor; and $260 was the price of a ton of dynamite. When the tunnel engineer finds that his bore is not to pierce hard-rock, of whose solidity he is more than reasonably assured, he prepares to use cutting-shields. These shields, proceeding simultaneously from the portals and from the footings of the shafts, are steel rings of a circumference only slightly greater than that of the finished tunnel. With pick and with drill and dynamite, they constantly clear a path for it, whereupon it is pressed forward in that path. Dummy tracks follow the cutting-shield; and dummy locomotives--more likely electric than steam in these days--are used in removing the material. Electricity has been a boon to latter-day tunnel-workers. Its use for light and power keeps the tunnel quite clear of all gases during the work of boring.