A Catalogue of the Collection of Cambrian and Silurian Fossils Contained in the Geological Museum of the University of Cambridge (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1873 Excerpt: ...relations of the Menevian (c), Ffestiniog (d), Tremadoc (e), and Arenig Groups (f) in the district around Portmadoc, N. Wales. By the Bev. A. Sedgwick, LL.D. 1847, and J. W. Salter, 1853--7. The faults are aU by J. W. S. The strata, in descending order, are: --f. Arenig (or Skiddaw) Group. Dark earthy slates on a base of sandstone ( = Stiper Stones, Shropshire). e. Tremadoc Group. Dark slates, iron stained, and with felspathic beds--1500 feet thick. d. Ffestiniog Group. Thick flaky sandstones, 2000 feet, and a bed of block slate 300 feet. c. Menevian Group. Dark slate and sandstone--only the top beds (with Olcnus cataractcs). Middle Cambrian, e. Tremadoc Group. N. Wales. S. Wales. (Sedgwick, 1847). e 1. Lower. Chiefly Black Slate. e 2. Upper. Sandstones, grey and bluish: iron beds: ferruginous slate, &c. e 1. Lower Tremadoc Slate (Salter, 1857). A natural continuation of the Upper Lingula Flags. Chiefly black slate, but very ochreous in part. The fauna is essentially Middle Cambrian, but shews a tendency to include some few Lower Bala types, such as Niobe, Psilocephalus, &c. The species however are all distinct, even from those of the Arenig Group, and those of the Upper are distinct from those of the Lower Tremadoc. We distinguish the upper, e 2, from the lower group, e 1. Case and Column of Drawers. Reference to Mccoy's Synopsis: and Figures of Genera. Names and References; Observations, (be. Numbers and Localities. TRILOBITA. Angelina Sedgwickii, Salter (Decade Geol. Surv. II. pi. 7). The most abundant of the Tremadoc trilobites: allied to Olenus, but with 15 body rings (Olenus has 14), and greatly larger than any known species of that genus. Even size is a character of some importance in classification. Occurs in all sorts of compressed shapes in...