Adam Clarke on Psalms 105:41

He opened the rock, and the waters rushed out - See the note on Exo 17:6, to which I can now add, that a piece of this rock, broken off by the hand of my nephew, E. S. A. Clarke, in the course of the present year [1822,] now lies before me. It is fine granite; and so well distinguished as a granite, that the feldt-spar, the mica, and the quartz, of which granite is composed, appear very distinctly. It is worthy of remark, that, as granite is supposed, in the most accredited systems of geology, to be the very basis of the earth, the original rock, and all other substances to be superimpositions upon it, and as the decompositions of the feldt-spar produce pure vegetable earth, this rock should be used for this purpose, and should be an emblem of Jesus Christ, the Creator and Redeemer of the human race; and that it should signify him who is the basis of all things; who upholds all by the word of his power; without whom nothing is stable, nothing fruitful; from whom alone the water of life proceeds; and in whose name only is salvation. And that rock (in the wilderness) was Christ! and it is the only remaining emblem of him in creation.