In working out, at the request of Sir Archibald Geikie, the petrography of the Lower Carboniferous Volcanic rocks in Haddingtonshire (the results of which I propose shortly to publish), I have been led to examine the igneous material that builds up the isolated hills (necks), situated on the margin of the volcanic area of the Garlton Hills. Among these, the rock of Traprain Law especially attracted my attention. It is a close-grained, dark brown to grey rock. Some varieties have a glistening or greasy surface, and are speckled over with dark spots, while others show glancing cleavage surfaces of a clear glassy felspar (sanidine).