282 J. E. MAKE ON TBTE CAMBEIAN AND 



Coniston. From these mudstones the following species were ob- 

 tained : — 



Ovarian capsules of Grraptolites ? i Monograptus tenuis. 



Monograptus convolutus, var. a, com- gregarius. 



munis. colonus. 



SedgwicTcii'i I Climacograj^tus teretiusculus'i 



They are seen near a millpond about 250 yards W.N'.W. of 

 the rectory, and curve round, so as to become exposed again in a 

 quarry close to the mill, which is further down the stream than the 

 pond and about the same distance from the rectory. Here about 

 15 feet of them are seen, but there is no indication of the top beds 

 being visible. In each place they contain thin bands of subordinate 

 grit. 



They are succeeded in ascending order by the Tarannon Shales 

 of the Survey, which are exposed in natural sections and in a quarry 

 near the farm of Tanygraig, just above the mill-pond. 



There are therefore three reasons for referring these beds to the 

 Graptolitic Mudstones : — Pirst, lithological character, which we 

 have seen already to be of considerable importance in comparing 

 the two areas. Secondly, stratigraphical position ; for these beds 

 occur between the Tarannon Shales, which have been correlated by 

 Mr. Aveline with the Pale Shales of the Lake district (Geol. 

 Mag. Decade ii. vol. iii. p. 282) and the gritty beds which Prof. 

 Hughes correlates with the Austwick Conglomerates. Thirdly, 

 palseontological affinity : of the Graptolites found, all save one are 

 characteristic Graptolitic-mudstone fossils in the Lake district ; this 

 one, Monograptus colonus, is characteristic of much higher beds, 

 the upper Coldwell beds, and supplies another instance of migration 

 from Wales to the Lake district. With regard to the palaeonto- 

 logical evidence, we can state at once, from tlie presence of Mono- 

 grapti, that the beds are Silurian ; for there is no well-authenticated 

 instance of a typical Monograjptus occurring in the Cambrian series ; 

 also we may infer, from negative evidence, that these beds are not 

 the equivalents of the Brathay Plags, for in that case Monograptus 

 priodon and M. vomerinus would certainly be among the first fossils 

 found ; but the only other Graptolitiferous beds in England about 

 this horizon are the Graptolitic Mudstones themselves ; consequently 

 there can be no doubt that these beds must be referred to that 

 series. 



Similar black beds are seen above the Corwen Grits of Nant 

 Caweddu, near Corwen. 



7. The Tarannon Shales. 



These beds have, as before remarked, been identified by Mr. 

 Aveline with the Pale Shales of the Lake district, which they 

 exactly resemble, except that, like the Graptolitic Mudstones of the 

 Dee-valley area, they are more cleaved than is usually the case with 

 the corresponding beds of the Lake district. 



