208 STKATIGEAPHICAL GEOLOGY 



Lower Devonian had some extension to the northward, but both 

 are absent above the Silurian outcrop in the Mendip Hills, which 

 are only 1 7 miles north-east of the Quantocks. 



Upper Devonian. In South Devon at certain places, as for 

 instance Plymouth, West Ogwell, and Chudleigh, the massive 

 limestones pass up into red or pink limestone containing 

 Acervularia Goldfussi, A. pentagona, and Ghonophyllum with some- 

 times Rhynchonella cuboides and Spirifer bifidus. In other places a 

 massive grey unfossiliferous limestone is succeeded by red shales 

 with layers of nodular limestone containing the characteristic 

 Goniatites (see p. 199) with Cardiola retrostriata and Phacops 

 cryptophthalmus. These beds are succeeded by red and green shales 

 in which the small Crustacean Entomis serrato-striata is often 

 abundant, with occasionally the small bivalve Posidonomya venusta. 



West of Dartmoor, in North Cornwall, these higher beds have 

 a much greater development, occupying a broad tract of country 

 extending from between Padstow and Boscastle on the coast round 

 the north side of Bodmin Moor to the borders of Dartmoor between 

 Tavistock and Bickleigh. They consist of grey, green, red, and 

 purple shales in which impressions of the Pteropod Styliola are 

 often abundant as also is the Entomis. Other fossils only occur 

 locally, but quarries near South Petherwin have yielded a large 

 fauna, the following being some of the species : Clymenia Icevigata, 

 C. striata, Orthoceras Phillipsi, Tornoceras linear e, Ctenodonta 

 antiqua, Cardiola retrostriata, Spirifer Verneuilli, Orthis interlineata, 

 Strophalosia subaculeata, and Phacops granulatus. 



In the cliffs on the west coast it has been possible to make out 

 something like a regular succession in spite of faults and plications. 

 The data on which this is based are given in the Survey memoir 

 on the country round Padstow, but the following table is not a 

 copy of that given in the memoir, as I have omitted the flaggy 

 slates of Camel Quarry, which may be of Middle Devonian age 

 and have separated the lower part of the " Striped Slates." The 

 descending succession then reads thus : 



5. Purple, green, and variegateS slates. 



4. Dark slate and pillow lava. 



3. Soft black slates with limestone bands (many fossils). 



2. Grey slates and thin limestones and a fossiliferous band yielding 

 many Cephalopoda. 



1. Grey shales with scattered phosphate nodules, thin layers of lime- 

 stone and of black grit. 



The phosphatic nodules in the lowest beds contain Conularia 

 complanata ; the limestone of Dinas Head (in No. 2) contains black 

 cherts with Kadiolarian remains ; while the overlying black slates 



