RT Journal Article SR Electronic T1 Thirty years retrospect of the progress in our knowledge of the geology of the older rocks JF American Journal of Science JO Am J Sci FD American Journal of Science SP 1 OP 21 DO 10.2475/ajs.s2-33.97.1 VO s2-33 IS 97 A1 Roderick Impey Murchison YR 1862 UL http://www.ajsonline.org/content/s2-33/97/1.abstract AB