My dear Sir

As you have thought the superintendence of the Admiralty Instructions worthy of the sacrifice of your time, I cannot hesitate a moment in undertaking the Geological part.—¹ I will do my utmost to make them worthy of your approval, though I confess that I feel great doubts how far I shall succeed. Should I fail, I hope you will get some one else to undertake the task, & any part of mine which was serviceable might be worked in without my name. It is a great relief to me, that you have the superintendence of the whole, for then I shall feel safe that nothing very unwise will left in, though I assure you that I shall be very far from taking less pains on this account. Unfortunately I am at present in the midst of a difficult dissection, which if I neglect, the labour of some weeks will be almost thrown away,² so that I fear that I cannot commence for about a week, but when I do I will do nothing else till I have finished.

I have already drawn up for Prof. Owen some remarks on Coral Reefs, & these, I think, ought now to come into the Geological part, of which I did not know when I wrote them.³ I fear my instructions will make rather a short Chapter.

I am extremely much obliged for your kind thought of my health, which is never now strong & which prevents me from working but a very short time each day;— I mention this, as you might suppose I could draw up the instructions in the intervals of other pursuits; but this I cannot do.—

Will you be so good as to present my respectful & kinds compliments to Lady Herschel, & believe me, my dear Sir, with the most sincere respect. | Yours very faithfully | C. Darwin To | Sir J. W. Herschel Bart.—