114 R. D. Roberts— The Tict-Eill Conglomerate. 



List of Fishes from the "Forest Bed Series." 

 (Those marked with an asterisk* are new to the " Forest Bed Series.") 



Perca fluviat'hs, Linn. 

 *Acerina vulgaris ? Cuv. 

 *Piatax JVoodwurdi, Ag. 



Hsox lucius, Linn. 

 *Barbus vulgaris ? Flem. 

 *Leuciscus cephalus ? Linn. 



* ■ rutilus, Linn. 



erythrcphthalmus, Linn. 



* Tinea vulgaris, Cuv. 

 *Gadus morrhua, Linn. 

 * pollachius ? Linn. 



Acipenser, sp. 

 *Galeus canis, Linn. 

 *Acanthias vulgaris, Bisso. 

 *R(ija hatis. 



Haja clavata. 



*Abramis brama, Linn. 



In bringing these notes on the " Forest Bed Vertebrata " to a 

 close, I desire to offer my best thanks to the gentlemen in charge of 

 public collections and those possessing private ones, who have so 

 freely placed their specimens at my disposal, thus enabling me to 

 compare them and to accomplish a task which would otherwise have 

 been im.possible. 



It is hoped that the memoir, of which these notes have been an 

 epitome, will now shortly be published by H.M. Geological Survey, 

 and will be found useful for future workers in this field. Much 

 still remains to be done, and doubtless new material will be 

 brought to light, which will enable us to trace more clearly than is 

 even yet possible, the changes of life which must have taken place 

 between the early Pliocene times and the Glacial and Post-Glacial 

 periods. 



V. — The Twt Hill Conglomekate and the Base of the 



Cambkian. 

 By B. D. Egberts, M,A., D.Sc. (Lond.), F.G.S., Clare College, Cambridge. 



A FEW words of explanation are required to enable those not 

 familiar with the Carnarvon district fully to appreciate the 

 importance of Prof. Bonney's confirmation^ of the view respecting 

 the age of the Twt Hill conglomerate first put forward by Prof. 

 Hughes, and afterwards advocated by myself.'* The controversy 

 possesses a general interest, apart from the fact that the strati- 

 graphical position of a certain bed is now fixed, inasmuch as it 

 shows how cautious it is needful to be in dealing with these ancient 

 rocks without the most thorough and careful mapping of the whole 

 area. 



In February, 1879, Prof. Bonney read his paper on " The Meta- 

 morphic Series between Twt Hill and Port Dinorwic " before the 

 Geological Society, and described the conglomerate in the Twt Hill 

 quarry. " The rock," he says, " exposed on the summit of Twt Hill 

 is at first sight like a coarse granite, which, however, is almost 

 without a micaceous constituent." " The lowest rock exposed in the 

 Twt Hill quarry is of the same type as that at Twt Hill. Above 

 it comes a bed with a similar matrix, containing pebbles in the 

 upper part, then a band of coarser conglomerate, the pebbles being 

 often full an inch in length. To this succeeds a band of finer 

 conglomerate, then coarser, and lastly another of finer, passing up 



1 See Geol. Mag. Jan. 1882, p. 18. 



2 See Geol. Mag. Vol. VIII. Dec. II. p. 194 and p. 439. 



