492 ME. W. A. E. USSHER ON THJ; DEVONIAN 



by the Eiver Teign opposite Combe Cellars. This concretionary 

 character, distinguishing the Knollen-Kalk, is locally developed in the 

 form of calcareous nodules in irregular dark-grey slates, as near 

 Lewell (Chudleigh), near Bishopsteignton, by the Teign west of 

 Combe Cellars, and west of Abbotskerswell. 



Above the Knollen-Kalk we encounter chocolate-red slates and 

 mudstones, containing Posidonomya venusta and Entomis, locally 

 greenish and grey. In addition to the localities mentioned by 

 Kayser, these beds, correlated by him with the Cypridinen-Schiefer, 

 occur in Kingsteignton Railway-cutting at Newton- Abbot, Anstey's 

 Small Cove, and Goodrington. In the district west of Newton- 

 Abbot the Upper-Devonian beds consist mainh' of red and greenish 

 slates, the latter furnishing badly preserved Goniatites at Wrigwell 

 House. 



Sporadic evidences of vulcanicity frequently render the relations 

 of the Upper and Middle Devonian extremely obscure, and outside 

 the limestone areas, where the normal slate type everywhere 

 prevails, the localization of these groups (as may be seen from a 

 recent communication to the Devon Association on the geology of 

 Tavistock) is extremely indefinite. 



The main distinctions between the lithological characters of the 

 three Devonian groups in the area under descrij)tion are as fol- 

 lows : — Lower Devonian : presence of grits and sandstones, often in 

 mass. 



Middle Devonian : slates, of grey and bluish tints ; fossils in 

 lenticles and much distorted, but not infrequent. 



Upper Devonian: slates, very unfossiliferous, red and pale 

 green tints prevalent. 



The common characteristics of the groups are : — 



Middle and Lower Devonian : slates in which the boundary can 

 only be ascertained by palaeontological evidence. 



Upper and Middle Devonian : massive limestones, in which no 

 hard-and-fast boundary-line can at present be traced by the dis- 

 covery of fossils ; local prevalence of volcanic schalsteins and tuffs, 

 breaking up the limestones and obscuring general indications of 

 boundary. 



§ III. Delations of the Culm and Devonian. 



No paper on the Devonian rocks of South Devon would be com- 

 plete without a reference to the relations of that formation to the 

 Culm-measures. Here it must be confessed that the details supplied 

 by this district are wholly inadequate to furnish even general con- 

 clusions of a trustworthy nature, the boundaries being in most 

 cases fault-lines. There are, however, certain known facts outside 

 the district available to supplement the meagre evidence within it. 

 HoU * advocated the existence of a considerable unconformity be- 

 tween the Culm and the Devonian rocks of South Devon, on the 



* Quart. Journ. Geol. Soc. vol. xxiy. 



