HARDWICKE'S SCIENCE-GOSSIP. 



171 



Much of Plymouth itself is paved with this stone, and 

 hence it is said that the town is paved with marble, 

 the beauty of which may well be perceived on a rainy 

 day, when the moistened stone best exhibits its 

 structure. 



Some of the choicest varieties of marble are dug in 

 the vicinity of Ipplepen, Newton Abbot, and St. Mary 

 Church. In this district, as well as at Plymouth, the 

 beds are sometimes specially distinguished by the 

 character of their organic remains. 



Thus the "Feather Stone" contains the coral 

 Favosites polyniorpha ; some varieties contain Cyatho- 

 phylluvi ciEspitosinii, Hcliolitcs porosa, Astrcea pcii- 

 iagona, &c., while the "Buck's Horn Marble" is 

 formed of Stroviatopora. Other varieties again are 

 noted for their colour or the peculiar veins of spar 

 which run through them, one of which is termed 

 "Thunder and Lightning." 



The disturbances to which the Devonian beds and 

 culm-measures have been subjected are worthy of 

 much attention. In some quarries it is impossible to 

 make sure of the dip of the limestone, it being 

 affected with a rude cleavage, and cut up by parallel 

 joints. In the grand cliffs of Torquay the contortions 

 may be seen to advantage, and Mr. Champernowne 

 has drawn attention to an inverted anticlinal, which, 

 apai-t from physical structure, is also marked by a bed 

 at the base of the limestone which contains Calccola 

 sandaliua. * 



At Hope's Nose, a quarry in the limestone shows 

 beds apparently horizontal resting on the upturned 

 edges of similar limestone, and this feature has been 

 produced by a fault which runs along the face of the 

 quarry with a hade dipping away from it. In the 

 culm-measures the contortions and faults are equally 

 numerous, so that it must be the labour of many years 

 and many lives ere the entire structure of Devon is 

 worked out in detail. 



Most of these disturbances were produced prior to 

 the accumulation of the Triassic rocks, and the beds 

 themselves must have been largely denuded before the 

 earliest sediments which mark this period were 

 deposited. 



The red sandstones, conglomerates, and breccias 

 of the Triassic period, which form the picturesque 

 cliffs at Dawlish and Teignmouth, occur in outliers 

 at Slapton, and at Thurlestone on the shores of Big- 

 bury Bay. At this last-named locality a natural arch, 

 formed of these rocks, stands out on the foreshore. 



No organic remains belonging to this period have 

 been found in the district, but pebbles of the Devo- 

 nian limestone washed out of the rocks are frequently 

 picked up on the beach at Teignmouth and Dawlish, 

 and are sometimes polished for brooches. 



Resting indifferently on any of the older rocks are 

 found the outliers of Upper Greensand which form the 

 Haldon Hills, and perhaps the crest of Milber Down, f 



* Trans. Devon Assoc, for 1874. 



t See Quart. Journ. Geol. Sac, vol, xxxii. p. 230. 



These are composed chiefly of sand of many colours, 

 green, red, and brown, with a few included sandy 

 and cherty concretions ; but there is no such develop- 

 ment of this upper cherty part of the series as we 

 meet further east at Chard and Lyme Regis. The 

 hills are, however, capped by accumulations of flint 

 and chert gravel, the relics of the chalk and of the 

 upper part of the Greensand which formerly extended 

 over the district. In the Greensand are found species 

 oi Aniiitonitcs, Trigoiiia, Exogyra, &c. 



In the valley of the Teign, between Bovey Tracey 

 and Newton Abbot, are certain clays and lignites 

 which contain plant-remains pronounced by Dr. Heer 

 to be Miocene. The details of the lignite-beds in 

 which these fossils are chiefly found, have been most 

 carefully worked out by Mr. Pengelly, and they are well 

 shown in a large pit near Bovey Tracey. Some of 

 the beds have been used as fuel during the past 150 

 years, -but the burning of the Bovey coal is almost 

 discontinued now. 



The clay beds, which are worked very largely in 

 the parish of Kingsteignton, are about 40 feet in 

 thickness, and are most probably older than the 

 lignites. Sandy beds are met with beneath them, 

 and the entire series must attain a thickness of about 

 300 feet. The clays are largely used in the manufac- 

 ture of pottery, &c. 



The formation itself, when looked at in a large 

 way, seems to have been deposited in a lake, the 

 slopes surrounding which were covered with a luxuri- 

 ant vegetation, comprising Wellingtonia, Cinnamons, 

 Evergreen Oak and Fig, Vines, Rotang-palm, numer- 

 ous Ferns and Water-lilies. Much of the sediment- 

 ary deposit was due to the destruction of the granite 

 hills, the felspars giving rise to the clay, and the 

 quartz yielding material for the coarse sands.* 



Far more recent deposits of gravel fringe this Bovey 

 basin, and extend up the hills on to Haldon. To 

 what exact period they belong is uncertain, but it is 

 probable that their formation may have taken place 

 during some of the changes which affected the 

 country during the Glacial period. Considerable 

 portions of them have been reasserted in modern 

 times by the river, and constitute parts of the "head" 

 beneath which the Bovey clays are worked. 



In the higher portions of the Dart valley are very 

 coarse boulder-gravels containing large masses of 

 quartz, quartzite, granite, and other rocks, which the 

 present stream would seem incapable of shaping or 

 transporting, t 



Mention should also be made of the China-clay 

 worked at Lee Moor, about five miles from Plympton, 

 which deposit, like the Bovey clays, owes its origin 

 to the destruction of the felspar in the granite. 



Among the most interesting of the geological 

 phenomena offered for our study, are the caverns and 



* Pengelly and Heer, Phil. Trans., vol. clli. 

 t See paper by W. A. E. Ussher, Trans. Devon Assoc, for 

 1876. 



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