540 MR. E. E. L. DIXON AND DK. A. VAUGHAN ON [Nov. 19H, 



In passing, it may be remarked that the sequence, Z-D inclusive, 

 is thicker collectively in South- Western Gower than at any other 

 place in the South- Western Province where it has been measured ; 

 and that D is more completely developed in this district, also, than 

 anywhere else in the same province. 



Earth-Movements. 



(4) The thicknesses, when combined with the depths at which 

 the deposits have been formed, in the manner outlined on p. 537, 

 paragraph (4), would enable us to compare the magnitudes in the 

 different districts of each earth -movement that accompanied 

 deposition. In our general ignorance of exact depths, this can 

 be done only for the summations of the various movements 

 between those horizons that appear to have been deposited at a 

 uniform depth in all districts. Of such horizons the most useful are 

 the lagoon-phases, on account of their well-defined character and 

 the certainty that differences between different districts (as regards 

 average depth of deposition of any phase) are negligible, the range 

 of depth in a lagoon-area being small. To apply the method : — 



The first datum-horizon is Km, which is probably developed 

 throughout Gower. By the time that the next datum-horizon, 

 the base of C 2 , x was initiated, Km had been buried more deeply in 

 the South-Western District than in North-Western or Eastern 

 Gower, by an amount equal to the difference between the thickness 

 of the deposits formed in the interval in the first district and that 

 formed in the others ; this difference, on the justifiable assumption 

 that K was no thicker in the North-Western and Eastern districts 

 than in the South-Western, was at least 300 feet (see Table I, 

 facing p. 505). In the interval between Km and the base of C 2 , 

 therefore, depression was greater, by at least 300 feet, in South- 

 Western than in North-Western or Eastern Gower. 



In the same way, by the time that the next datum-horizon, the top 

 of S 2 , was reached, the base of C 2 had been buried at least 400 feet 

 deeper in the South-Western (see, however, previous footnote) and 

 Eastern Districts than in North- Western Gower. And, if the radio- 

 larian cherts at the base of P are a lagoon-phase and may, therefore, 

 be regarded as a datum-horizon, by the time that their deposition 

 was commenced the top of S 2 had been still more deeply buried in 

 South-Western and Eastern than in North-Western Gower. 



(5) Erom the preceding conclusions it is seen that the earth- 

 movements that accompanied deposition were differential and that 

 the regions of deeper water were the more depressed. 



On the assumption 2 that the differential movements were wide- 

 spread tilts, not irregular faulting or folding, the axis about which 



1 In South-Western Gower the base of C 2 is not a lagoon-phase, but the 

 fact that it is there represented by deeper-water deposits only emphasizes the 

 conclusion that follows. 



2 That assumption is justified, in the case of the Upper Avonian movements, 

 by the fact that throughout those movements the Eastern and South-Western 

 Districts were depressed 'pari passu. 



