I have visited the Lizard on three occasions, namely, in 1887 in company with several Members of the Geologists' Association under the able guidance of Messrs. Howard Fox, F.G.S., and E. A. Wiinsch, F.G.S.; in 1888 by myself; and in February of the present year in company with Mr. Howard Fox, to whom I feel under the greatest obligation, his intimate acquaintance with the Lizard rocks and his local knowledge rendering his aid in the field extremely valuable. On each occasion I collected numerous specimens of the rocks, and studied thin slices of them under the microscope during the intervals between my visits, so that I have had an opportunity of correcting the impressions made in the field by microscopic work in the study, and of again testing ideas formed in the study by fresh observations in the field. I have examined under the microscope over ninety thin slices of my own specimens, nearly fifty have been lent me by Mr. Howard Fox, and Mr. J. J. Harris Teall kindly placed those of his own collection at my disposal. Before stating the results of my own investigations I think it desirable to refer briefly to the views expressed by previous observers. Sir Henry De la beche's opinion may be gathered from the following extract from his ‚Report on the Geology of Cornwall and Devon ‚∗:— "if it were not for the occurrence of the hornblende slate in the conglomerate of the Nare Point, we might suppose that it [the hornblende