LOWER SLATES AND GREAT DEVON LIMESTONE. 1 33 



containing many eruptive rocks, especially towards their lower 

 part. In a well-boring in Fleet Street, Torquay, the thickness of 

 the limestone was proved to be 130 feet, and that of the underlying 

 slates 185 feet. The Lower Slates occupy the country between 

 the Ashburton and Bickington ranges of Limestone, and between 

 those of Dartington and Ogwell ; but their total thickness cannot 

 be estimated. 



At the base of the Limestone, the passage-beds (red shaly lime- 

 stones) contain the zone of Calccola sandalina at Daddy Hole, 

 Torquay, at Mudstone Bay, at Brooking, near Dartington, and at 

 Chircombe Bridge, near Newton Abbot. Below comes the zone 

 of Cyrtoceras bdellalifcs at Mudstone, east of Brixham, and IVIeadfoot 

 near Torquay. A specimen of Scaphaspis cormibicus was found by 

 Lieut. Wyatt-Edgell at Mudstone Bay. 



The beds of Lammerton, north of Tavistock, were placed by j\Ir. 

 Etheridge about this horizon. 



The total thickness of the Limestone at Dartington is estimated 

 at 450 feet by Mr. Champernowne ; but the thickness is subject to 

 much variation. 



In the Devonian Limestone, we find many points of resemblance to the Car- 

 boniferous Limestone. Some beds are of a dense blue colour, with few veins of 

 calcite ; others again are very freely veined with a fine network of spar, or 

 contain broad bands of crystalline matter. Beds of nearly white limestone occur 

 near Ideford, others again are oolitic in structure. The beds often occur in great 

 wedge-shaped masses, suggesting irregular accumulation. It may be remarked, 

 also, that many of the beds of Devonian Limestone, when fractured, emit the 

 same sulphureous smell as does the Carboniferous Limestone ; while the slaty 

 beds beneath sometimes exhibit similar alternate bands and nodular beds of 

 limestone. The limestone is sometimes dolomitic. 



Sedgwick and Murchison noticed the occurrence of " thin laminje of bright 

 coal '' in the limestone near Plymouth.^ Mr. Godwin-Austen too observed that 

 "the limestone of the Ashburton band is exceedingly carbonaceous, containing 

 even seams of anthracite," and he detected the same feature at Totnes. About 

 six feet of black carbonaceous shale has been noticed by Mr. Champernowne at 

 Skinner's Bridge, near Dartington. The formation of the carbonaceous matter 

 may have been due to marine rather than to terrestrial vegetation. - 



The weathering of the Devonian Limestone is naturally similar to that of the 

 Carboniferous Limestone. Some of the honeycombed surfaces that may be seen 

 on joints and exposed edges of the rock in a quarry at Wolfsgrove Farm, near 

 Kingsteignton, showed that when fossils occurred, they stood out in relief in the 

 cavities, proving that here at least the phenomena resulted from the action of 

 atmospheric agents, and not that of snails. (See sequel.) 



The Limestones of Chudleigh, Ashburton, Ogwell, Ipplepen, 

 Berry Pomeroy, Dartington, Totnes, Brixham, Torquay, Petit Tor, 

 Babbacombe, St. Mary Church, and Newton Abbot ^ (the Great 

 Devon Limestones) are as well known for their purely economic 

 value for marble, building- and paving-stone, as some bands of the 

 rock are for the richness of their palseontological contents. 



^ Trans. Geol. Soc, 2nd series, vol. v. p. 651. 

 * Godwin-Austen, Idem, vol. vi. pp. 461, 469. 



^ The name of the village of Newton Bushel, well known as a locality for 

 Devonian fossils, is now merged in that of Newton Abbot. 



