On the night of August 19, 1779, there occurred on the south side of the North Mountain about ten miles northwest of Carlisle a geological phenomenon that eventually drew the attention of the astronomer David Rittenhouse, Dr. Benjamin Franklin, the Secretary of War, and the president of Harvard College, and was described both in private letters among these and other men and also in the published proceedings of the second oldest learned society in the United States. More than two centuries later the site of this unusual natural event is known at least in a general way to older residents of the Cumberland Valley.
The Carlisle Deluge, as one geologist has called the episode, was a sudden, powerful gush of water from the mountainside that carried all before it on its descent to the Conodoguinet Creek, tearing large trees out by their roots, sending great rocks tumbling over one another, flooding fields and pastures, and leaving behind a gash or ravine whose traces were visible after more than two centuries.
How a report of the incident reached Philadelphia is not known. It was probably by a private letter for no Philadelphia newspaper in the two months after the event seems to have noticed it. In any event, his curiosity aroused, Rittenhouse travelled to Carlisle in mid-October1 and spent a day inspecting the area where the deluge occurred and the evidences it had left. Several possible explanations occurred to him, but none satisfied him. Guessing that there might have been an electrical cause, Rittenhouse described the deluge in a letter of April 29, 1780, to Benjamin Franklin, his fellow-townsman then in France, and asked his judgment on the phenomenon.
Sir: Amidst the many important objects of your attention I doubt not but you sometimes unbend your mind by an Excursion thro' the fields of Philosophy [science]. I shall therefore make no apology for communicating to you a freak of Nature which seems to be new, at least it is so to us. On the 19th. of August last during a heavy Shower of Rain, not attended by any Thunder lightning or wind, a prodigious Torrent fell on the North or Blue Mountain 10 Miles from Carlisle, and Carried away every Rock and Tree however large that stood in its Course, it likewise tore up the Earth & Stones from 4 to I 0 feet deep, and from two to 6 perchers wide, for upwards of 100 rod, that is from very near the top of the Mountain down to the foot of the first Steep Ascent.
I had heard such wonderful accounts of the effects of this Cataract that I was induced to take a ride of 130 miles to view the Spot, and spent a whole Day there with satisfaction and astonishment. The facts I am perfectly convinced of by my own observation, and which appear to me most worthy of your notice are these. It was certainly a stream of water falling from the Clouds in a Spot not above 10 yards in diameter, and not any collection of waters falling in rain, on the surface of the Earth. The face of the mountain will not admit a possibility of supposing it to have been a collection of water already fallen in rain in the common way, it being a very high narrow ridge, and the Soil, Stony, Sandy and sufficiently porous to drink up rains falling in the common way. And tho' the Stream seems to have continued some time, certainly at least a few minutes, it nevertheless fell invariably in the same Spot, without moving to the right or left. I should be happy in having your opinion on this matter, my own Conjecture is that a Great Quantity of the Electric fluid, passing silently from the Cloud to the Mountain, carried the forming drops of rain from all quarters of the Cloud to one point, and by uniting them produced this prodigious Cataract.2
Franklin's reply, if he made one, seems not to have survived.
On December 16, 1780, at a meeting of the American Philosophical Society in Philadelphia Rittenhouse read a letter that he had written to Franklin; it is described in the secretary's minutes as
containing conjectures founded on accurate observation, with respect to changes which the Globe of the earth in some parts hath undergone, most probably by the falling of [tantalizingly the sentence is uncompleted].
The observations are principally confined to the Western district of Pennsylvania.3
For nearly half a century until his death on January 2 at the age of 85 Milton Embick Flower was the best informed, most authoritative, and most widely known historian of Carlisle and Cumberland County. He was the author of books, monographs, and catalogues that recorded and interpreted the past of this area, and, in the words of one of his successors as president of the Cumberland County Historical Society...