The Base of the Silurian Near Haverfordwest

Extract

On several previous occasions the author has described in the pages of the Geological Magazine certain fossils from so-called “Slade Beds” from the roadside near St. Martin's Cemetery, Haverfordwest. A large collection of fossils has been made by Mr. V. M. Turnbull from this particular locality during the last few years and presented to the Sedgwick Museum. From a prolonged study of this material and comparison with the typical fauna of the Slade Beds as described by Messrs. Marr & Roberts, the conclusion has been forced upon me that we have here to deal with a higher palæontological horizon than the true Upper Bala of this district, and that there is much more reason for putting it in the Silurian than for keeping it in the Ordovician. The stratigraphical evidence which has subsequently become available is in support of this view. A list of the fossils from this bed may be useful at the present moment, particularly as the Sedgwick Museum possesses by far the most extensive series which has been collected from it (see opposite page, 537).

The rock in which they occur is a greenish-grey, fine-grained, argillaceous mudstone with occasionally minute specks of mica and a little arenaceous material, but usually of a very uniform smooth texture. It breaks in an irregular, often subconchoidal manner, and is devoid of any regular or weil-marked planes of division. Exposed surfaces and the fossils themselves are generally more or less iron-stained. In appearance and general characters it is difficult or impossible to distinguish the rock from the higher beds of the Slade Series, but the fauna is completely different.