HA RDWl CKE 'S S CI£JV CE - G OS SI P. 



169 





A SKETCH OF THE GEOLOGY OF PLYMOUTH AND THE 



NEIGHBOURHOOD, 



Bv HORACE B. WOODWARD, F. G. S. 



Of the Geological Survey of England and Wales. 



HE country around Ply- 

 mouth possesses very 

 many features of geo- 

 logical interest, afford- 

 ing a good school for 

 the beginner, and fur- 

 nishing plenty of pro- 

 blems for the most ad- 

 vanced student. Repre- 

 sentatives of the three 

 great divisions of the 

 stratified rocks can be observed within easy distance 

 by road and rail ; and many exposures of both igneous 

 and metamorphic rocks can be reached with equal 

 readiness. The formation of the scenery is a subject 

 which opens up a number of interesting questions, 

 and leads us, when we come to study the records of 



Devonian strata to be concealed by the shales and 

 grits of the Culm-measures.* Turning eastwards, 

 we find outliers of the red sandstones, breccias, and 

 conglomerates of the Triassic period, which beyond 

 Torquay form part of the great belt of red rocks 

 which stretches across England to the mouth of the 

 Tees. 



Again, in the neighbourhood of Newton Abbot 

 are traces of the Upper Greensand ; and in the Bovey 

 valley beneath, occur the well-known clays and lignites 

 classed as Miocene. Extensive beds of gravel are 

 locally met with ; the coast-line is fringed here and 

 there with i-elics of raised sea-beaches and sub- 

 marine forests ; and the caverns, formed in the 

 Devonian limestone, have yielded the bones of 

 mammalia, many of them belonging to extinct forms, 

 associated with the ancient implements of man. 



Dartmoor. 



Ivy Bridge. 



Plympton. 



River Plym. 



Plymouth. 



^Vy'V"' ^--'-r ^^T^^^^^^^^^^^^^^l l ^;^^^!^^^^^ 



Granite. 



Altered Slate. Igneous Dyke. .Slates. 



Fig. 147. Section from Dartmoor to Plymouth (after Sedgwick and Murchison). 



^'Hr-. 



Limestone. 



the caverns, into close connection with the early 

 history and antiquity of man. Speaking generally, 

 the rocky structure of Plymouth and its neighbour- 

 hood is composed of limestones, slates, and sandstones, 

 which belong to the Devonian period. The rugged 

 highlands of Dartmoor are formed of granite ; while 

 numerous igneous rocks, contemporaneous and in- 

 trusive, jut out here and there amongst the old slates 

 and limestones. 



Westwards, near Mevagissey, we find traces of 

 Upper Cambrian (or Lower Silurian) rocks ; and if 

 we turn to the north and north-east, we find the 



No. 152. 



But while the relative ages of the rocks have, on th 

 whole, been well established, yet the geology of 

 Devonshire presents, perhaps, more problems in 

 regard to tlie classification of its strata than any 

 other English county. Some of the hardest geological 

 battles have been fought over the Devonian rocks ; 

 and whether they entirely correspond in age with 

 the Old Red Sandstone, or belong partly to this 

 formation and partly to the Lower Carboniferous 



* The term Culm is a local name for anthracite, and the 

 beds in which it occurs are classed with the coal-measures and 

 millstone grit, 



I 



