falling from the 165 fathom level to the 180 fathom level; the cause could not be ascertained with certaintity, but it was supposed that the deceased while retiring from his work place for protection from his own blasting and his partners holes sat upon a piece of timber which had, perhaps, been loosened by stones from former blastings, which gave way; he had no occasion to trust his weight to the timber; it was not intended for any such purpose