In a memoir on the geology of Martha’s Vineyard contained in the 7th Annual Report of the Director of the U. S. Geological Survey, I gave a preliminary account of the several deposits, mostly of doubtful age, exhibited on the western part of that island. The conclusions there presented were in the main those which had been derived from a study of the district in the years between 1860 and 1872. Since this memoir went to press, I have been able considerably to extend my studies in this field. A portion of the results of this latter work are embodied in a recent paper entitled, ‘‘On the Occurrence of Fossils of Cretaceous Age on the Island of Martha’s Vineyard, Mass.’* In that paper I have endeavored to prove the existence of middle or lower Cretaceous deposits in the central portion of that island. About 15 species of fossils . . .