140 DEVONIAN. 



Corals, mostly in a bad state of preservation, but presenting a 

 Silurian facies.' (See p. io6.) 



Ladock Beds. — These beds are the most recent of the rocks of 

 Central and West Cornwall, and are so named from the parish of 

 Ladock, north-east of Truro. They extend to St. Agnes Head, 

 and over the country around St. Columb, Padstow, etc. They 

 consist of dark-grey or blue and sometimes yellowish slates, or 

 schists, together with beds of sandstone, conglomerate and quartzite. 

 The sandstone has become much silicified in places, and there it 

 forms an excellent road-metal. The Halebote rock in the parish 

 of Creed is composed of this sandstone. The conglomerate forms 

 a remarkable bed, stretching from Nare Point towards Trelo- 

 warren: some of its included masses of hornblende-slate, and 

 quartzite, weigh several tons. The thickness of the Ladock Beds 

 is estimated by Mr. Collins at from looo to 1500 feet. They 

 do not include any limestones, and no fossils are recorded from 

 them in the area he has described.^ 



5. LONDON AREA. 



In some deep well-borings in and near London, rocks of Old 

 Red Sandstone and Devonian age have been identified. (See 

 account of Well Sections.) 



Purple shales, with fossils of Devonian type, were met with in 

 the boring at Turnford, near Cheshunt. And at Meux's Brewery, 

 Tottenham Court Road, London, mottled red, purple, and light 

 green micaceous shales, with thin seams of red and grey quartzite, 

 were proved. From these beds Mr. Etheridge identified Spirifera 

 disjimcta, Rhynchonella cuboidts, Edfuondia, Orthis, and Chonetes. 



Red sands, sandstones, and clays were proved in a deep boring 

 at Kentish Town. These beds, formerly grouped as Lower Green- 

 sand, are now regarded as probably Upper Old Red Sandstone by 

 Prof. Prestwich. 



At Crossness, near Erith, beds of hard quartzose sandstone and 

 red and grey shale were reached. These are grouped as Old Red 

 Sandstone or Devonian by Prof. Prestwich.* 



At Richmond variegated sandstones and marls were reached, 

 and these are grouped (doubtfully) as Poikilitic by Prof. Judd, but 

 are regarded as more probably Old Red Sandstone by Prof. Prest- 

 wich.* A specimen in the Museum at Jermyn Street appears 

 to more closely resemble the latter rock. 



Mr. Whitaker is of opinion that the red rocks at Kentish Town 

 and Crossness may belong to the New Red Sandstone (Poikilitic) 



1 I2tli Report Cornwall Polyt. Soc. p. 66; G. Mag. 1868, p. 568, see also 

 p. 247 ; Sedgwick, Q. J. viii. 2 ; W. Pengelly, Report R.G.S. Cornwall, 1850, 

 p. 116, and Trans. Devon Assoc. 1868. 



■ journ. Roy, Inst. Cornwall, vii. (1881). 



^ Q. J. xxxiv. 913 ; see also E. Hull, G. Mag. 1881, p. 508. 



* Q. J. xl. 749, 762. 



