W. A. E. Usaher — Fakvozoic Rocks of Devon and Somerset. 443 



structure of North Devon and West Somerset, established a basis 

 for a more philosophical and extended classification. Prof. Hull in 

 1878 sent an article to the Geol. Mag. in which he accepted Mr. 

 Etheridge's general classification, and Prof Jukes's correlation of 

 the Pickwell Down Series with the Old Eed Sandstone, but regarded 

 the Foreland Group as equivalent to the Dingle and Glengaritf grits, 

 bridging over the unconformity between the latter and the Old Red 

 Sandstone by a Marine Devonian series composed of the Morthoe 

 and Ilfracombe slates and shales, the Hangman grits, and the Lynton 

 grits and schists. 



In 1879 Prof. Hull read before the Geol. Soc. of London a paper, 

 in which he maintained on evidence the unconformity of the 

 Glengariff grits to the Old Eed Sandstone, and the overlap of 

 Carboniferous strata upon them, and correlated the Glengariff 

 grits with the Ludlow series of the West of England and the 

 border of Wales. 



In 1880 Prof. Hull further applied his views, correlating the 

 Irish section with that of Devon as proposed by him in 1878, main- 

 taining the identity of the Pickwell Down Sandstones with the 

 Upper Old Red and with the Psammite de Condroz of Belgium, and 

 of the Foreland Grits with the Dingle and Glengariff Beds, as 

 Upi^er Silurian. 



Notwithstanding the vast amount of literature that has been 

 written on North Devon and West Somerset, comparatively little 

 attention has been paid to the stratigraphical relations of the beds 

 apart from considerations of correlation with rocks elsewhere, upon 

 palceontological grounds. Even Mr. Etheridge's paper left much 

 to be done in this respect and failed to explain the changes which 

 the various divisions undergo when traced from west to east, 

 and more particularly left unsolved the relations and extent of 

 the Lower Devonian beds. To supply this need I have neglected 

 no opportunity of ascertaining the relations of the older rocks in 

 North Devon whilst engaged on a survey of the superficial deposits 

 on behalf of the Geological Survey, and, having to study them in 

 West Somerset with reference to the bordering Triassic districts also, 

 succeeded in constructing a geological map of the area upon Sheets 

 27, 26, 20 and 21, of the Ordnance Maps. Of these, Sheets 20 and 

 21 have been mapped in detail as well as the defective topography 

 would allow; but in Sheet 27, points of junction, established by 

 coast work and numerous traverses up the courses of the principal 

 streams, have been joined up. Sheet 26 contains a very small part 

 of the Devonian area, and, like 27, has not been surveyed in detail. 

 An abstract of the notes made during these surveys would make a 

 paper of very considerable size, the notes themselves being sufficient 

 to form a monograph upon the stratigraphy of North Devon and 

 West Somerset of considerable bulk. I purpose, therefore, to give 

 the briefest possible outline of the results obtained, taking the 

 divisions seriatim from the Foreland rocks upward. 



The divisions are as follows : — 



Lower Devonian \ ^^^^^^^^ Grits. 



Lyatou Beds — Grits and Schists. 



