184 REPORT— 1866. 



extended to more than forty species. Their distribution remains precisely 

 the same as that elaborated in the last Eeport. The greater number of 

 species occur with the largest Parado.vides, P. Davklis, -which is the upper- 

 most of the three forms knoTvn ; P. Ilulsii occurs at the base of the really 

 dark shnles, close upon the grey beds of the Harlech group just mentioned, 

 in which group, 200 feet down, lies, as before noted, the P. Aurora. 



It is worth notice that these three species, with their accompanying 

 smaller forms {Conocornphe, Theca, Agnostus with each), keep close to their 

 own particular domains, the species of Paradoxldes being never found mixed 

 together. This may serve to show how veiy perceptible a change of fauna 

 may occur within moderate limits ; for the section is perfectly continuoiis, and 

 yet these TrUobites are confined to narrow bands and do not reappear. 



A species of Orthis, Avith few large plaits, has been found this year, the 

 minute predecessor of aU the OrtJiis tribe. Hitherto nothing but horny 

 species of Brachiopods {Lingida and Dixcina) has been known to occiu- in 

 these old beds ; and one or other of these go dovra to the very base, while the 

 Orthis is only found above the limit of the highest Panidoxides-hc(is. 



[Tlie fossils exhibited gave a general idea of this old fauna ; a much 

 larger series is sent to the British Museum and Jermj-n Sti-eet.] 



.3. "With respect to the Ffestiniog group, or true Lingula-flag beds, we find 

 this formation occupying its right place, at the very top of the Mencvian 

 group. It occurs in a faulted patch in A\Tiitesand Bay ; and forms a bold but 

 narrow syncUual at the mouth of Solva Harbour and the Cradle Eock. It 

 also occurs, of diminished thickness, in the district lying between the granite 

 of Brawdy and Asheston and the syenitic axis. Upon it lies a trough of — 



4. Trcinadoc Ucds, or what we regard as such. They have only this 

 year been worked out fully. And lying as they do upon the ti-ue Lingula- 

 fiag and under the Arenig or Skiddaw slate, they can hardly be anything 

 but Tremadoc beds. They graduate by insensible degrees from the Lingula- 

 Sandstones, first as bluish-grey slate, and then earthy grey thick-bedded rock 

 of a peculiar tough texture, and contain the following fossils : — 



C'ahjmene, 2 species. 



Homalonotus, 1 species. 



Asaplius, a giant species and a smaller one, the former all but undistin- 

 guishable from the Asaphus Homfragi of the Tremadoc rocks. 



OrfJioceras, with peculiar arched str'je. 



jS'ucida or Ctcnodonta, 2 or 3 species. 



Orthis Carausii, a coarse-ribbed fossil, highl}- characteristic of these beds. 



Orthis, a fine-ribbed species like 0. elcgantula. 



Bellerofhon, Lingida, Obolella. 



Now this fauna is wholly unlike the deep-water fauna of the Tremadoc 

 region. It is evidently a thin formation, depoeited in much shallower water 

 and this may be the reason of the great change in the fauna. 



But there is something peculiar in the absence of the recognized ujjper beds 

 of the Lingula-Jlags as they exist in North Wales. Instead of a recurrence 

 of black slate for the Upper Lingida-jlags and lower portion of the Tremadoc 

 grovp (forming a very thick set of formations deposited in deep water), we 

 have only a thin series of comparatively shallow water accumulatioiis, 

 marked by abundance of worm-tracks, and the fossils above quoted. This 

 gives a marked character to the series, and indicates the following succession 

 up to this point : — 



