§ 10. RAILWAY SECTIONS. 497 



and abounding in mines of lead and zinc; and at a yet 

 greater distance, mountainous tracts in which roofing slate 

 abounds and mineral veins yet more valuable ; and lastly, 

 he will often find, surrounded by these slaty tracts, central 

 groups of granitic rocks." 



The Great Western Eailway, from London to Bath, and 

 the Birmingham line from Euston Square to Derby, respec- 

 tively traverse the strata comprised in the oolitic system ; 

 for our present purpose the former will afford the most 

 instructive illustration. From the Paddington station, 

 which is situated on London Clay (p. 229,) the line 

 passes along tertiary strata, by Ealing, Hanwell, and 

 Slough, and enters the chalk near Maidenhead ; beyond 

 Wallingford it traverses the clays and limestones of the 

 Oolite, and the cuttings in many places exhibit good 

 sections of these deposits. Near Bath it emerges on the 

 Lias, and crossing a narrow belt of Triassic strata, passes 

 on to the Carboniferous beds of the Bristol coal-measures. 

 In this route there are several localities of considerable 

 interest, as Faringdon, Swindon, Chippenham, Calne, &c. 

 to which we shall allude hereafter.* 



10. Subdivision of the Oolite : — Portland Oolite. f 

 — Beds of limestone, having the structure above described, 



* See Medals of Creation, vol. ii. Geological Excursions to Clifton, 

 p. 922 ; and, for the section exposed by the Birmingham and Derby 

 line, Excursions to Matlock, p. 933. 



Mr. Hugh Miller contrasts the appearance of these railway sections, 

 in consequence of the low angle of inclination in which the secondary 

 strata in England generally lie, with those of Scotland, as laid bare in 

 the line from Glasgow to Edinburgh. There every few hundred yards 

 in the line brings the traveller to a trap rock, against which the strata 

 are tilted at every possible angle of elevation. 



t For details of the geological phenomena exhibited by the beds 

 below the Chalk, and above the Xew Eed sandstone, in the South-east 

 of England, Pr. Fitton's elaborate memoir, in the Geol. Trans, {new 

 series) vol. iv. should be consulted. 



