206 STRATIGRAPHICAL GEOLOGY 



the whole of the North Devon rocks were duplicated by the 

 fault, the Pickwell Down Beds being a repetition of the Foreland 

 Beds, and the succeeding beds on each side of the fault being 

 comparable with one another. This view was combated by Mr. 

 Etheridge, 2 who found it easy to show that the fossil evidence 

 made it untenable, for the fossils of the Lynton Beds are 

 unquestionably Lower Devonian, while all the fossils found in beds 

 south of the Pickwell Down Group are with equal certainty of 

 Upper Devonian or Carboniferous age. 



When Mr. Etheridge wrote, no fossils had been found in the 

 Morte slates, but in 1895 and 1897 Messrs. Hicks and Whidborne 3 

 found fossils at several places along their outcrop, and the 

 assemblage appears to indicate the existence of a Lower Devonian 

 fauna. In the papers referred to Dr. Hicks stated his belief that 

 not only is there a fault along the southern boundary of the 

 Morte slates, but one along their northern border, that these 

 slates are in fact thrust up between the two lines of fault, and that 

 they are the oldest rocks in North Devon, but the final conclusion 

 is not generally accepted. It is true that the Morte slates differ 

 from any other slates in North Devon, for they are smooth and 

 glossy, while the Lynton slates are mostly rough and gritty ; still 

 it is more probable that they are a facies of the Lynton slates than 

 beds older than the Foreland sandstones. 



The fossils referred to were obtained from Morte Bay and 

 Mullacott on the coast, and from Treborough in Somerset. Some 

 of the species are described as new (such as Lingula mortensis) ; 

 some resemble Silurian forms, such as Orthis rustica ; and others 

 are Lower Devonian, e.g. Dalmanites laciniatus, Strophomena 

 tceniolata, S. explanata, Chonetes plebeia, and C. sarcinulata. 



Middle Devonian. In South Devon this consists of a series 

 of grey shaly slates in which masses of limestone are lenticularly 

 developed, and in places both are partially replaced by volcanic 

 materials stratified tuffs and diabase lavas. 



The chief interest centres in the limestones, and. these are best 

 known from their developments at Plymouth, Brixham, Torquay, 

 Totnes, Ipplepen, and Ogwell. The lowest beds, however, are 

 always grey shales, and under the lowest limestone near Torquay 

 these have yielded Calceola sandalina, Spirifer speciosus, Sp. 

 curvatus, Atrypa reticulata, and some other fossils. They evidently 

 correspond with the beds known as Calceola shales in Belgium. 



The limestones certainly occur on more than one horizon, and 

 Mr. Ussher has classified them as lower and higher limestones. 4 

 The lower set are generally dark grey or nearly black, are well 

 bedded, and consist mainly of crinoid ossicles, beds containing corals 



