tributed in thin layers. The only other recognizable fossil which occurs in the rock is the so-called Dictyocaris ramsayi, which occurs in considerable abundance" (145, 151). If one searches in the literature back to the time when eurypterid remains were first found in the Pentland Hills, one comes upon a description which is in but poor accord with the most recent one, emanating from the Scottish Survey, although bearing out quite well the statement made by Laurie. John Henderson in 1880 read a short account before the Geological Society of Edinburgh of some fossils which he had discovered in the Pentland Hills, in the beds in the Gutterford Burn. A few extracts from his paper will serve to give the clearest description which I have yet found of the eurypterid-bearing band. "This bed, which is upwards of a foot in thickness, is mostly made up of what I consider to be a mass of vegetable matter, along with an organism which has been described and figured by Mr. Salter . . . . as a large phyllopod crustacean under the name of Dictyocaris ramsayi . . . . there is in this bed a large amount of vegetable matter, some of the plant remains showing about one-tenth of an inch of carbon on the surface, and these plant remains are so associated with the supposed crustacean remains that it is difficult to determine the one from the other. I am now inclined to believe that the Dictyocaris is of vegetable origin. The fact of finding plant remains in such abundance in the Silurian rocks is, as far as I am aware, a new feature, as until lately true plant remains in that formation were considered doubtful. But there can be no mistaking their character and abundance in this bed, which is so thickly charged with carbon that it looks like an impure bed of coal . . . . the remains of undoubtful crustaceans of the genera Eurypterus and Stylonurus in a fair state of preservation occur in the same bed with the Dictyocaris and plant remains . . . . the bed in which these specimens are got must be at least as low as the Wenlock Shale. It lies several hundred feet below the fossiliferous bed in the North Esk above the reservoir, which is of undoubted Wenlock age" (115).
We do not know precisely the exact relation between the eurypterid-bearing bands and the beds containing the other fossils, but all available evidence indicates that they are not identical. Considering the decidedly different facies associated with the eurypterids and with the remaining fossils it seems probable that the former are confined to certain bands or lenses, as is often stated. In any case their occurrence is still capable of easy explanation whether they are actually
