The Lower Silurian rocks of Scotland, largely developed as they are in the south, and in spite of the great labour that has been bestowed upon them, are by far the least known of all the fossiliferous formations of that country. While the maps of the Government Geological Survey are coloured in all the subdivisions of the strata of the other formations included in their area, the Lower Silurians are merely indicated by a common purple tint, and not the slightest attempt at a subdivision is made. Even the single bed of Limestone they contain, below the horizon of that of the W. coast, is doubtfully referred to the Llandeilo, and the sign of interrogation is carefully placed before its title. Nicol, Harkness, J. C. Moore, and many other eminent geologists, have worked different portions of these ancient deposits since the publication of “The Silurian System,” but as yet very little progress has really been made in correlating its different parts with those of the type formation of the sister country.