Does anyone know if the full text of a letter that Elizabeth Wallace included only in part in her book, Mark Twain and the Happy Island has been published anywhere?  If it has, could you tell me where?  I need to cite the portion she left out from a Jan. 26, 1910 letter to her from SLC. 
The full quote I need to find is:
"Do I 'know more' than I knew before? Oh, hell no!  There was nothing to learn (about hereafters and other-such-undesirables), there never has been anything to learn and know about those insulting mysteries. I am happy--few are so happy--but I get none of this happiness from 'knowing more' of the unknowable than I knew before."
 
She has it as "No, revelation--of a valuable sort--does not come through sorrow when one is old. . . . I am happy--few are so happy--but I get none of this happiness from 'knowing more' of the unknowable than I knew before."
 
What I am interested in, of course, is represented by those "dots."
 
Thanks,
Sandra Uetz