Monday Evening 18 Apl. 1808.
Not untill about two hours since at Our election did I worthy Sir receive Your favour of the 3th. for which Misfortune I am indeed extremely Sorry, happy should I be to see You at my poor dwelling Once more. this time in particular, but if that cannot be, pray let me know the hour You will be at Our Ct House, and I will be there and describe the Manner of Constructing Your Mill dam, which if pursued, or Nearly pursued will not wash away, nor very Materially decay for Thirty Years. at the Rappahannock Ironworks the River has a Narrow passage with amazing rapidity between two Steep Rocky hills. at that place in the Year 1772 I erected a Dam percisely the hight which You have described Yours, which Dam (except the Tap log which has been since Renew’d) is without any other expence now Standing firm & intire, altho the expence thereon was not at first proportionably near as much as Yours must at once building have cost. that is, according with Your description of it; nearly as high up Stream as below, there is the error, that has been the defect and cause of its destruction.
My Dams are not raised up stream any more than I can possibly help, On such a bottom as the Bed of the River on which Your dam rests, Long large hew’d logs should be laid from One side of the River to the Other Longitudinally, another Row in like Manner 15 feet distant from them further up the River and in a parallel line with the first Row or line of Logs, from One of those line of Logs to the other Cross pieces of Timber which we call Ties at the distance of Eight feet from One another Should be well Dovetaild into them lines of logs forming at Right Angles sort of Penns as You have been pleased to call them. So far I presume Your director and I agree. Then I lay on Another Row of Logs on the down Stream line, and then put in as before Another set of Ties Dove tailing them to the line of up Stream logs at midway between the first ties, and so right a cross to the second line of logs down Stream which for distinction I call the front of the Dam; thus, then the Dam will be two logs high in front and one log high up Stream, the up stream line of logs having two sets of Ties Dovetailed in it. Then as before laying another line of logs in front and also Another line of logs up Stream. but now take notice that the second line of upstream logs is not to rest on the first but to lay down on the bed of the River by the side of them immediately up Stream which will Receive Your third Set of Ties which must be the thickness of a log longer than the first or Second Set. Your Dam will then be three Logs high in front and but One log high up Stream then proceed with Your fourth Log in front and its Ties as with Your Second Here ends the direction of the timber Work of Your Dam. that is the front logs being previous got a Size sufficient to Raise Your Dam as high as it is Needfull. N.B. The two last set of Ties will perhaps be 20 Inch or two feet longer than the two first. the ties should be of good White oak and Nearly as large in Size as the length way Logs, or they will not admit of a good Dovetail tinnon at each end, much depends on the care and Workmanship of this part, the ties are not only to be let into the logs below them, but they are also carefully to be let into the line of logs above them, that is in front, that is half the thickness of the Tie goes into the log below and half thereof into the log above, and so with every one of them in front.
The Stone Work should commence as soon as the first Row of Ties are put in and be performd by Masons or some handy Men who understands building a Stone Wall and laid in layer by layer with great care and going over each layer of the Wall as it progresses, with Small Stones and Very Course gravell Carefully filling up ever Chink Joint and Vacancy between the Stones untill the Wall be completely fitt’d and perfectly solid, and so on, layer by layer, untill the Wall be Very Nearly Levell that is Nearly as high up Stream as below, reserving however some of the largest and best Blocks of Stone for the last layer, then instead of the Monstrous Quantity of Earth You Mention on the upper side, let Small Stone be put in Smaller and Smaller untill it arrive at the Size of Very Course Gravell. I then put in a layer of Straw or Ceader bushes Neatly thatch’d and put on a coat of Mud if it can be had, or Rich Soil, not very Material, tho’ any sort of gravelly or Muddy Stuff will do, I use no plank for Spoiling as it is call’d or any other purpose about the dam, it is too buoyant, may serve to Swim or float off the Dam but do no good whatever! pray pardon this hurried Scrawll if I have the honor of conversing with you I can better explain it. Yr. most Obdt Hble Serv.
[Postscript in Dupl:]
the Uncertainty of the letter [. . .]ing You with which I presumed to trouble You on the 18th. has induced me to forward a copy; if you cannot come this way conveniently, I shall be proud and happy in waiting on you at Any pointed hour at Our Court house. A post rider from Washington City on his rout Westwardly passes my Dwelling Home every Wednesday, by Him if you please to give me directions they shall be Obey’d with pleasure and promptitude—I am with all due regard
Worthy Sir, Your very hble. Servt.
DLC: Papers of Thomas Jefferson.