On the Monian and Basal Cambrian Rocks of Shropshire

§ I. Introduction In my memoir “On the Monian system” as developed in Anglesey, I suggested that the Longmynd rocks might belong to the Upper Monian, on account of their general similarity to those of Bray Head, and that the Uriconian rocks of Dr. Callaway might be Middle Monian, because they were at once Precambrian and Volcanic. As these suggestions, which would be of some importance if true, were matters of conjecture only, I have taken the first opportunity to examine the district with care in order to arrive at a definite conclusion. At the time of my writing, it was the universal opinion that the Longmynd series were essentially, even if not typically Cambrian ; but about the same date Dr. Callaway was suggesting to the local geologists of Shropshire that in view of the break that existed between his "HoUybush Sandstone," which he regarded as Menevian, and the Longmynd series, it was doubtful if the latter were really Cambrian, and he proposed that till this was decided, they should be called Longmyndian. The same argument was more strongly enforced last year by Prof. Lapworth, who writes, “the presence of Olenellus in the (Comley) Sandstone appears at first sight to fix distinctly the Precambrian age of the so-called Uriconian rocks of the Wrekin and their English equivalents, and even to render the Precambrian age of the Longmynd a matter of fair probability.” It will be seen that in both these cases the age of the Longmynd rocks was made