I have duly recieved your favor of the 3d & thank you in advance for that of a copy of your observations when they shall be published. there always existed a doubt whether the source of the Savanna was not North of the 35th degree, which your labors have now removed. a great deal is yet wanting to ascertain the true geography of our country; more indeed as to it’s longitudes than latitudes. towards this we have done too little for ourselves, & depended too long on the antient & inaccurate observations of other nations. you are wiping off this reproach, and will, I hope, be long continued in that work. all this will be for a future race, when the superlunary geography will have become the object of my contemplations. yet I do not wish it the less, on the same principle on which I am still planting trees to yield their shade and ornament half a century hence. with my best wishes for the success of your labors, accept the assurance of my great esteem & respect.

Th: Jefferson