14 W. A. E. Ussher — The Culm of Devonshire. 



Again, the peculiar baked appearance of the Coddon Hill beds is 

 more or less local, although appearing at such wide intervals as the 

 Northern and Southern Culm Measure areas, wherein their character- 

 istic appearance was severally noticed by Phillips ; and the lime- 

 stones may be said to occur in them, the reddish even Goniatite 

 shales of the West Leigh area belonging to this group. 



Eeferring to the Coddon Hill beds, pp. 189, 190, Phillips says : — 

 " The beds, which in this range overlie the shales and limestones of 

 Swimbridge and Venn, are a whitish or grey or black chert in thin 

 striped beds. . . . "With these lie white arenaceous and argillaceous 

 layers, mostly very soft, and sometimes cleavable, other parts show 

 black and reddish shales. In these laminated beds lie Goniatites, 

 Orthoceratites, Terebratulee, and Posidoniee. The debitumenized 

 condition of these white shales parallel to the black bituminous 

 shales of Swimbridge is remarkable; aud it is a fact repeated not 

 only on the Northern range near Bampton, but also on the southern 

 range near Launceston and Lew Trenchard. In a quarry on this 

 range near Tawstock, Major Harding found Turbinolopsis pauci- 

 radialis" (Petraia celtica). 



To take one or two examples from many furnished by my notes : 

 The Yenn limestones are exposed in two adjacent quarries ; in the 

 smaller one they are very much disturbed, being probably affected by 

 two faults ; they appear to overlie beds of the Coddon Hill type. In 

 the larger quarry even-bedded dark grey limestones dip 35° W. ; at 

 60°, they are interleaved in places by shaly parting. One of the beds 

 is covered on its surface with impressions of Posidonomya (Posidonia) 

 lateralis, and less frequently P. Becheri and P. tvbercidata. 



Near Eastcorabe, west of Tawstock, thin beds of fine grit and thick 

 shale of whitish buff and dark grey colours, split up by numerous even 

 ioints into small angular pieces, are quarried for " gravel." The 

 joints, as is usual in beds of the Coddon Hill type, are local contrac- 

 tion-cracks of individual beds. 



The flexures and contortions of this series are too numerous to 

 furnish any generalized observation as to the relations of the beds, 

 and space fails me to enter into local details. 



In the south of the area, notwithstanding the local repetition of the 

 calcareous horizon, and of beds equivalent to the Coddon Hill series, 

 there is some difference in the general characters of the Lower Culm 

 Measures ; thus slaty grey shales which, from their typical exposure 

 on St. David's Hill, Exeter, I have called splintery shales of the St. 

 David's type, are by no means uncommon in them, also beds of a 

 nodular or concretionary character ; the grits vary from thin and even, 

 to rather thick irregular beds. 



Phillips thus describes the Lew Trenchard section : " Argillaceous 

 and arenaceous laminar beds, white or coloured by oxide of manganese, 

 which correspond to those of Coddon Hill in North Devon, contain 

 Calamites, Aster ophjllites, Neuropteris, and a Goniatite, . . . below are 

 quarries of black limestone" with " shaly partings rich in Posidonice" 

 in the upper part. No Goniatites found in ^the limestone. Phillips 

 points out the occasional presence of oolitic structure in the limestones 

 of this series. 



