This year is the hundredth anniversary of the birth of one of the world's greatest mineralogists, Samuel Lewis Penfield, who was born January 16, 1856, at Catskill, N. Y., and died August 12, 1906, at South Woodstock, Conn. Despite the fact that his death after three years of illness with diabetes cut short his career when he was at the height of his ability, Penfield left a record of remarkable achievements. These had brought him fame and the esteem of his contemporaries. What is more remarkable, the passing of half a century has not dimmed their luster. It is not fair to judge work done fifty to eighty years ago by comparison with what we know today, but Penfield's work can stand such a comparison.