GEOLOGY OF THE BKISTOL COAL-FIELD, 315 



Another weU-marked faulfc is met with in the Wick Kocks, and 

 interfering with the beds of coal, as seen in fig. 15. 



Fig. l5.— TFtck Fault. 



a Devonian. — b Carboniferous Limestone.— c Millstone Grit. —<^ Lower Coal 

 Measures, — e Trias.—/ Lias. 



Other examples are to be met with, but not so well displayed. 

 It is probable that these faults were caused by internal forces 

 beneath the crust of the earth about the commencement of the 

 Triassic period. At any rate, dreadful as were the results to the 

 then existing surface, yet they were the means of bringing within 

 our reach the rich stores of coal. Many of the coal seams lay so 

 deeply that, had not this upheaval of the country taken place, we 

 could not possibly have reached them. 



Another variety of the disturbance of strata occurs very frequently. 

 A large mass of older rocks are forced up to the surface throu^-h 

 those of later age. We have already noticed some as of Silurian at 

 Purton {pa^e 263), and at Tortworth (pa^e 267) of Devonian as at 

 Erockley Combe {pa^e 268), and of Easalt at Downhead (pa^e 270), 

 As seen in fig. 16 representing the rocks through which the 

 "Wickwar tunnel passes, 



Fig. 16. — Wichvar Anticlinal 



a Devonian, —b Carboniferous Limestone. — c Lias. 



