^6 UPPER CAMBRIAN (ORDOVICIAN). 



recognized the rocks and fossils as similar to beds developed in 

 Normandy.^ Orthis Biidleighensis also occurs, and this, together 

 with pebbles of similar quartzites, have been found in the Triassic 

 pebble-bed of Budleigh Salterton, and in the Drift of the Midland 

 counties.^ 



These rocks have been more recently studied by Mr. J. H. 

 Collins, who describes them as a great series of dark grey or blue 

 schists and conglomerates, estimated to have a thickness of 23,000 

 feet. In his opinion they extend much further into West Cornwall 

 than has been supposed, since they may be traced southward to 

 St. Keverne, and westward to Penzance and Mousehole. They 

 comprise thick beds of quartzite, and also thin lenticular masses 

 of black limestone, siliceous slate, etc. Conglomerates may be 

 seen at Nare Head. Quartzites yielding fossils have been found in 

 the Meneage peninsula, south of Helford river. The limestones 

 which contain fragments of Encrinites and species of Orthoceras are 

 found north of Porthalla, at Gerran's Bay, Caerhayes, and Gorran 

 Haven. ^ Graptolites have been found by Mr. Peach in the dark 

 slates of Black Head. 



Economic Products, etc. of the Bala or Caradoc Beds. 



Murchison observed that in the Caradoc sandstone, remains of fossils are often 

 so abundant as to render some of the beds sufficiently calcareous to be burnt for 

 lime: these beds are known to the workmen as 'Jacob's Stones.' Sandstone is 

 quarried at Soudley, Horderley, and Long Lane near Craven Arms. There are 

 limestone quarries at Esquire Hall, near Bishop's Castle. 



Some valuable deposits of phosphate of lime (phosphorite) have been dis- 

 covered at the top of the Bala Limestone in the Berwyn Mountains, near Dinas 

 Mowddwy, between Llangynog and Bala, and near Llanfyllin in Montgomeryshire, 

 North Wales. Mr. D. C. Davies has described the bed as varying from 9 to 18 

 inches in thickness, it is composed of nodules, some of which still preserve 

 their organic structure.* (See also p. 59) Beds of jasper also occur at Dinas- 

 Mowddwy, and other places. 



Mr. W. Keeping observed nodules showing cone-in-cone structure on the coast 

 between Aberystwith and Borth. They occur in Bala (?) or Lower Llan- 

 dovery rocks. ° 



Welsh oilstone is obtained from Bethgellert, and the vicinity of Llyn Idwal, 

 Snowdon, and sometimes called Idwal stone. From Snowdon the ' Cutler's 

 green stone ' is also obtained. Hones or oilstones generally consist of a fine- 

 grained and compact slate-rock ; they are sometimes called Whet-slates or 

 Whet-stones. 



1 G. Mag. 1864, p. 9. See also Jukes, Roy. Geol. Soc. Ireland, 1867. 

 - T. Davidson, G. Mag. 1880, p. 339, and Supplement to Devonian Brachiopoda, 

 Palreontograph. Soc. ; T. G. Bonney, G. Mag. 1880, p. 406. 

 •^ Journ. Roy. Inst. Cornwall, vol. vii. (1881). 

 * P. G. Assoc, iv. 566 ; G. Mag. 1867, p. 251 ; Q. J. xxxi. 357. 

 5 G. Mag. 1878, p. 532. 



