ORIGIN AND DEVELOPMENT OF ORE-DEPOSITS. 311 



to be of post-cretaceous date (Delabeche, Eep. &c., p. 290.) It 

 is quite probable that these N.S. faults have their counterparts 

 in the newer N.S. cross-courses of the mining district to the 

 westward. 



To the N. of Exeter near Killerton Park there are E.W. 

 faults which are post-permian or post-triassic (Delabeche, p. 

 294), but probably older than the N.S. faults just referred to. 

 The Upton Pyne manganese deposits occur parallel to the 

 Killerton Park faults and let down the new Red Sandstone. 

 In the Mendip Hills, the existence of a N.S. pressure acting 

 subsequently to the deposit of the lias (?) is shewn by the E.W. 

 ridges or anticlinals. 



12. — Still newer E.W. fissures appear to have been produced 

 in Tertiary times, thus the " slides " are referred to this period 

 by Delabeche. Near Bridport and Weymouth there are E.W. 

 faults which are probably of this period, i.e. those of the Isle of 

 Wight flexures ; at any rate they are of post-cretaceous date. 

 They may very probably be contemporaneous with some of the 

 slides mentioned (See Delabeche Eep., 313, 314). Still later 

 alluvial faults have been formed in a few — perhaps in many 

 places, but being mostly of small extent, they would easily escape 

 observation. 



There is little reason for supposing that any of these 

 upheavals or fissurings were of a specially violent character. 

 The initial strain in each case was caused by the elevatory 

 movements, the actual Assuring was an effect of gravity, and 

 may have occasioned notable earthquakes, but the subsequent 

 re-openings and " descents of the hanging wall," although 

 frequent, may have been on each occasion only a fraction 

 of an inch in extent — giving rise only to earth tremors of little 

 intensity,* as already suggested. 



*Eespectiiig the formation of the great chain of the Alps, Lyell writes :— > 

 "Talking of Escher and upheaval, I was not a little pleased to find how 

 thoroughly he goes with me in doing things slowly. 



No one in Europe is so well acquainted with the stupendous folds and 

 inversions of strata in the Alps, and yet he believes it all took place without any 

 interruption of the habitable state of these mountains. Had man been there, 

 he thinks he would not have known what was going on." 



Sir Chas. Lyell, Life, p. 255 (Aug. 1857.) 



