490 MK. W. A. E. U6SIIEK OX THE BEVONI Al<r 



M. Frecli kindly furnished me with the names of fossils found 

 iii the different localities visited. 



I have great pleasure in acknowledging my indebtedness to MM. 

 Gosselet and Barrois, and subsequently to J)r. Kayser, for their 

 kind and prompt assistance m identifying fossils sent to thera from 

 time to time in 1880. 



I am indebted to M. Tschernyschew for the assistance afforded 

 me, by the presentation of his admirable contributions to the 

 Devonian geology of Kussia ; and to MM. Gosselet, Kayser, and 

 Barrois for similar favours. 



My friend Prof. Gosselet devoted a week last September to con- 

 ducting me over the typical sections of the Ardennes rendered 

 classic by his investigations. His kindness supplied me with more 

 information and encouragement than I can hope to repay. 



§ II. Geinteral Description. 



The area to which this paper more particularly refers lies north of 

 the River Dart and East of Dartmoor, and comprises the most 

 complex and lithologically varied tract in South Devon. 



We naturally turn to the limestone districts to obtain evidence 

 of structure. Owing, however, to crushing, it is impossible to 

 obtain persistent and reliable dips beyond the actual exposures ; 

 and the acceptance of apparent superposition of limestone on slate, 

 or vice versa, in any one place must lead to endless confusion in its 

 general application, as inversion is rather the rule than the 

 exception. 



Evidences of strati graphical relations are often so dubious as to 

 suggest alternative explanations, such as anticlinal or synclinal 

 inversion or consecutive sequence. Moreover the sharp plications 

 often displayed in a single quarry, in beds otherwise exhibiting low 

 dips, inspire caution. 



\Yhen, however, we regard the district as a whole, the local 

 development of limestones in the Kingsteignton, Ip^jlepen, King s- 

 Kerswell, Torquay, Yalberton, and Brixham districts, — the preva- 

 lence of slates in the Berry-Park and Staverton districts, — and of 

 volcanic materials north-east of Bickington, south of Totnes, and 

 east of Yalberton. compel us to ascribe the anomalous distribution 

 of the limestones to very irregular accumulation dependent on 

 locally favourable conditions. Thus, in the area south of Totnes 

 the formation of limestone has been restricted, owing to a long- 

 continued period of volcanic activity ; whilst near Bickington, 

 Dartington, and Yalberton its accumulation has been partially 

 arrested from a similar cause. Again, in the Broadhempston 

 district the limestones are clearl)" impersistent ; and the Plymouth 

 and Yealmpton masses, although equivalent to the Ipplepen and 

 Denbury limestone, and to that of Ashburton, are, in the intervening 

 district, represented by slates with very occasional, insignificant 

 patches of limestone. 



A^'ithout such a broad interpretation as the above it is found that 



