4S8 MR. 0. X. J0XES OX THE HARTEELL-VALENTIAX [XOV. I909, 



small tributary enters from the north (F. 14). The graptolites 

 are beautifully preserved in full relief in pyrite, and occur in 

 great abundance. The following forms have been identified : — 

 Monograptus atavus (c), M. aitenuatus, M. cyphus (s.s.) v.c, M. 

 gregarius, M. inopinus (?), M. revolutus and var. austerus, M. san- 

 dersoni, Orihograptus mutabilis (v.c.), 0. cf. penna, Glyptograptus 

 tamariscus (c), Climacograptus hughesi, and CI. tornquisti (c.). The 

 strata between the two layers of calcareous nodules may be called 

 the zone of Monograptus cyphus (or cyphus zone), after 

 that graptolite which appears to be almost confined within these 

 limits. 



The upper layer of nodules ushers in a new set of beds, readily 

 distinguished by their lithological and faunal characters from the 

 underlying strata. They are exposed on both sides of the river 

 south-west of Ty'n-y-ffordd Farm, but are more easily reached on 

 the west side where they dip west-south-westwards at 25° to 35°. 

 The section shows alternations of massive blue mudstones and 

 dark-blue shales which are abundantly graptolitiferous : each band 

 containing some forms peculiar to itself, as well as others which are 

 common to more than one band : — 



Thickness in feet inches. 



(9) Pale greenish mudstones, with sandy stripes ; only 



lower part seen. 

 (8) Dark-blue graptolitic shales and mudstones, with a 



pale-green flag near the centre 2 6 



(7) Greenish-blue thickly-bedded mudstones, somewhat 



darker than 9 23 



(6) Dark-blue mudstones, with graptolites , 6 



(5) Blue flags and mudstones 3 



(4) Dark-blue ferruginous shales ; graptolites abundant . 4 6 



(3) Blue mudstones, with a layer of calcareous nodules 



about 2 inches in diameter at the base 3 6 



(2) Dark-blue ironstained shales, with flags of a paler 



colour, especially in the lower part ; graptolites 



throughout 20 



(1) Blue thickly-bedded mudstones 6 6 



Layer of large calcareous nodules (up to 1 foot in diameter). 



The mudstones intervening between the dark graptolitic shales 

 ■are decidedly paler in colour, and contain relatively few and ill- 

 preserved graptolites, which are, therefore, difficult of identification. 



From the lowest shale band (2) the following forms were obtained 

 (F. 15)': — Monograptus atavus (c), M. attenuatus, M. communis, 

 M. concinnus (c), M. cygneus (?), M.fimbriatus, M. gregarius, M. re- 

 volutus (v.c.) and var. austerus, M. sandersoni, M. triangidatus 

 and var. (c), Orihograptus cf. bellulus, Glyptograptus tamariscus, 

 Petalograptus palmeus, Climacograptus hughesi, CI. tornquisti (v.c), 

 Orthis(?J, and fragments of Orthoceras or Conularia. 



The most characteristic form is a variety of Monograptus tri- 

 angidatus, which has shorter and blunter thecse than is considered 

 typical. The graptolites are preserved in low or in full relief. 



The next higher shale band (4) afforded the following forms 



