Vol.65.] HARTFELL-VALENTIAN SUCCESSION AROUND PLYNLIjtfOJT. 499 



much influence, as the total thickness of the group does not differ 

 materially from that calculated elsewhere. 

 The section is as follows • — 



Approximate thickness in feet. 

 (15) Smooth blue flags, with thin black-banded grits at the top. 



(14) Dark-blue smooth flags 3 



(13) Smooth blue flags 10 



(12) Soft shales, weathering deeply in rusty-yellow colours... 8 



(11) Smooth blue flags 20 



{ 10) Shales, weathering to a deep rusty brown 6 



(9) Smooth blue flags, with a shale-band about 30 feet up... 55 



(8) Bronze-weathering shales 2 



(7) Pale-blue flaggy mudstones 20 



(6) Ironstained shale-band 1 



(5) Pale-blue flaggy mudstones 25 



(4) Shales, weathering to a deep rusty brown with a bronzy 



lustre 4 



(3) Greenish-blue flaggy mudstones, somewhat striped with 



sandy layers 8 



(2) Shale band 2 



(1) Mudstones like No. 3 15 



Leptotheca band. 



In band No. 2 I found hut a single specimen of Monograptus 

 convolutus ; in No. 4 (F. 33) that species occurred abuudantly, 

 together with If. ansulosus, If. limatulus, If. lobiferus (?), and 

 Climacograptus sp. In No. 6, I could find no graptolites, but 

 No. 8 yielded several species, among which the following were 

 identified:- — Rastrites hybridus, Monograptus ansulosus, If. decipiens, 

 M. limatulus, M. lobiferus, If. regidaris, Climacograptus hughesi, 

 and CI. tomquisti, the last-named being exceedingly abundant. 



The shaly band No. 10 is highly cleaved, and the only species 

 that I could identify were Monograptus tenuis (which occurred in 

 profusion) and Climacograptus hughesi. 



No. 12 yielded Monograptus decipiens, Climacograptus hughesi, 

 and a few others, while from No. 14 I obtained only Monograptus 

 sedgwicki. 



Thus, in a vertical distance of 130 feet, one passes from the 

 base of the pale mudstone group to the characteristic band with 

 Monograptus tenuis, which ushers in the zone of M. sedgwicki. 

 The most conspicuous fossil in the lower part is Monograptus 

 convolutus, and those beds may, therefore, be referred to that zone. 



In this section I was unable to obtain fossils from the shales and 

 black-banded grits which commence near the waterfall at the head 

 of the ravine ; but, on following them southwards along their 

 strike for about 200 yards, the grit debris at the foot of a small 

 crag yielded Monograptus becJci, If. nudus, M. runcinatus, M. tur- 

 riculatus, and fragments of dendroid graptolites, an assemblage 

 agreeing closely with that from the Fuches-wen quarry. 



A few yards down the slope is an old quarry in massive flags, 

 which are some distance below the black-banded grits. Forming 

 the top of the quarry (F. 35) are rusty ironstained shales about 

 6 feet thick, which are crowded in the lower part with Mono- 

 graptus tenids. They are underlain by about 20 feet of smooth 



