Collections 184A, 206, 203, and 204 (page 3 of request form) contain archaeocyathids and are of Cambrian age. The archaeocyathids are somewhat similar to corals in external form but can be easily differentiated in section. These will be reported on by another specialist.

Collections 71, 82, 211, and 631 contain no recognizable corals. These will be reported on by specialists in the fossil groups that are present.

Collections 48B contains abundant bryozoans, and coll. 83 and 632 contain a few. These will be reported on by a National Museum specialist if they are identifiable or if they contribute additional age data.

The following collections contain the corals indicated. Ages are based on the presence of certain structures in the scarce rugose corals and on the ranges of tabulate genera unless otherwise indicated.

Discussion: The tabulate genera Alveolites and Cladopora are limited to the Silurian and Devonian. In addition a moderate to large assemblage of Favosites and branching tabulate corals is indicative of the same age. So Silurian-Devonian is relatively easy to recognize on any decent sized collection of tabulate corals. However, these same corals cannot be used to differentiate between Silurian and Devonian or to recognized subdivisions of either, except in a very few places where species have been described and their ranges are well known.

Chain corals (Halysites, etc.) are often present in Silurian collections, but are not known in Devonian ones. Since they are absent from your collections I would suspect that most of them are Devonian, rather than Silurian.

Rugose corals (solitary or colonial horn corals) are of much more use in recognizing Silurian-Devonian subdivisions than are the tabulates. In the above collections, all of my finer age “guesses” are based on rugose coral genera which are limited to one system or series.

On the basis of this collection I would suggest the following for future consideration:
1. Collect tabulates as here, but recognize that these are of broad age value only.
2. Hunt for chain corals (Halysites, etc.) as these are all pre-Devonian.
3. Collect a variety of rugose corals where common, all possible ones where rare. If they are decently preserved they can be very good indices.