The most remarkable spring, however, is one located on the right bank of the river, some seven miles below Hollidaysburg. The peculiar feature about this spring is the fact that it ebbs and flows with the same regularity the tides do. The admirer of natural curiosities may arrive at it when it is brimming full or running over with the purest of limestone water; yet in a short time the water will commence receding, and within an hour or two the hole in the ground alone remains. Then a rumbling noise is heard up the hill-side, and soon the water pours down until the spring is again overflowed.
In the town of Williamsburg, on the property of John K. Neff, Esq., there is a remarkable spring. It throws out a volume of water capable of operating a first-class mill, together with other machinery, although the distance from the spring to the river does not exceed the eighth of a mile.
At Spang's Mill, in Blair county, is by far the largest spring in the upper end of the valley. It has more the appearance of a small subterranean river breaking out at the hill-side than that of a spring. It is about three hundred yards long, varying in width from one hundred to one hundred and fifty feet. The water has a bluish-green tinge, and is so exceedingly pure that a drop of it placed under a microscope would show fewer animalculæ than a drop of river-water would after being filtered. Formerly it contained thousands upon thousands of the finest brook trout; but of late years the number has been considerably diminished by the sportsmen who could obtain permission from Mr. Spang to entice them from their element with the tempting fly. A hundred feet from what is considered the end of the spring, there is a large grist-mill driven by its waters, which empty into the eastern reservoir of the Pennsylvania Canal, after traversing a distance of about three miles. Within two miles from the head of the spring, its waters furnish motive-power to two grist-mills, a saw-mill, and four forges.
As a singular circumstance in connection with this subject, we may mention that, within the memory of some of the older inhabitants, a considerable stream of water ran through the upper end of Middle Woodbury township, Bedford county; but the spring at the head of it gave out, as well as several other springs which fed it, and now scarcely any traces of it remain.