LETTER FROM HON. C. C. CLAY, JR. Washington, May 21, 1860. MY DEAR SIR: Severe illness, which has confined me to my room for ten days, has prevented my answering your letter sooner. And such is my prostration at this time that I feel I am not equal to the mental or physical effort necessary to reply fully to each of the questions you suggest. The action of our delegates in the Charleston Convention meets my cordial approval. It evinced a fidelity to principle and an unconquerable intrepidity in its maintenance that merits the admiration. and gratitude of every true Southern heart. I am happy to state that their course is approved by nearly all the Senators of the seceding States(I am not sure that I should except one) and a large majority of the Representatives of those States. I know it it is approved by four of my colleague-Messrs. Moore, Curry, Clopton, and Pugh.