530 ME. 0. T. JONES ON THE HAETEELL-VALENTIAN [Nov. I9O9, 



characteristic of the Gelli Beds, coupled with the abundance of 

 Monograptus turriculatus which only occurs rarely in those beds. 

 So closely do the lithological characters and the rest of the fauna 

 agree, however, that one is forced to compare the two sets of 

 deposits ; though it would seem that the physical conditions under 

 which the Gelli Beds were laid down may have commenced at a 

 somewhat earlier stage in the Cardiganshire district. 



The Bhudduant Group in its lithological characters strongly 

 recalls the beds about the base of the Talerddig Grits of Tarannon ; 

 but the critical graptolites of those grits have not been found, while 

 Monograptus turriculatus still survives, a suggestion again that the 

 lithological changes occur at lower horizons than in the Tarannon 

 district. 



The higher beds of the Talerddig Grits are probably represented 

 to the south of the Ystwyth Valley, and therefore outside the limits. 

 of the district here dealt with. It is of some interest that in the 

 hills some 6 or 7 miles south-east of Tregaron, and some 12 miles 

 south of the Ystwyth, this great grit-group is succeeded by purple 

 and green beds precisely similar in character to the Dolgau Mud- 

 stones which succeed the Talerddig Grits ; but, as no fossils have 

 been obtained from them, I cannot say whether they correspond 

 palajontologically to those mudstones. 



As to more distaut British areas, the Pont Erwyd succession 

 shows several points of agreement with the Stockdale Shales of the 

 Lake District, despite the great difference in the actual thickness of 

 the corresponding deposits in the two areas. The same fossils 

 occur in the same order in both districts, and to a certain extent 

 the same types of lithological change may be observed at correspond- 

 ing horizons, especially in the zones of M. fimbriatus, M. convolutus, 

 and M. sedgivicki. In these zones, it is possible in certain cases to 

 identify individual bands of graptolitic shale by means of their 

 fauna. Of these the leptotheca band, equivalent to the argenteus- 

 band, and the tenuis [=discretus'] band near the base of the 

 sedgwiclci zone may be quoted as examples. In the middle of the 

 argenteus band a peculiar thin pale-greenish band, called the ' green 

 streak ', was observed to persist over a wide area in the Lake 

 District. It is rather remarkable that, as noted in this paper, a thin 

 flag of a peculiar pale greenish-grey was found to occur near the 

 middle of the leptotheca band wherever that band was investigated. 

 A further remarkable resemblance is shown by the strong jointing 

 of the lower beds of the Monograptus convolutus zone. 



When the graptolites of the South of Scotland are revised in the 

 light of recent investigations, it will be possible to institute a very 

 close comparison between them and the Welsh deposits. As this 

 has been done as far as possible for the Rhayader and Tarannon 

 districts, it is unnecessary to go into it again for the Cardiganshire 

 deposits which agree so closely with the latter. 



