182 PROF. T. T. GROOM ON THE GEOLOGICAL [Feb. I9OO, 



Upper Coal Measures; and that the Permian beds were laid down 

 upon the latter ' with some amount of local unconformity/ * 



We have, therefore, evidence of the continuation in a northerly 

 direction of the Hercvnian folds. Whether or not the primary 

 movement during Coal-Measure times was more important than 

 later movements in the Trimpley district it appears difficult at present 

 to determine. Further investigations on the relation of the newer 

 and older Coal Measures of the district may be expected to throw 

 light on the subject. 



XVII. The Connexion between the Upthrusts or Over- 

 thrusts of the Archfean Massif of the Malverns and the 

 Overfolding of the Beds to the West. 



A close relation is discernible in the district of the Malvern 

 Hills between the elevation of the Archrean massif and the over- 

 folding of the Cambrian and Silurian beds to the west. This 

 relation is clearly brought out in the accompanying map (PI. VIII). 



It will be seen from the map that the western margin of the area, 

 over which the beds are vertical or iuverted, in most places tends 

 to follow the western border of the Archaean, whatever may be the 

 horizon of the beds so affected. This shows, on the one hand, that 

 the overthrust or upthrust was to a certain extent independent of the 

 disposition of the ordinary folds ; and, on the other, that it had a 

 close relation to the process of overfolding. It would appear 

 that the beds were first folded, and then overfolded along an axis 

 somewhat oblique to that of the normal folds, and that the over- 

 folding culminated in overthrust of the Archaean massif. A note- 

 worthy feature of this movement is the very high inclination of the 

 fault : this in some places is nearly vertical ; indeed, it is only in 

 the Malvern Tunnel that the fault can be actually proved to be 

 a thrust-plane having any considerable hade. The movement has 

 been in fact, to a certain extent, a simple upthrust. 



The amount of inversion of the Silurian strata in several localities 

 diminishes towards the thrust-plane. Examples of this are seen 

 west of ]S T orth Hill, where the greatly inverted beds at a little 

 distance from the fault, on approaching the latter, tend to become 

 vertical (see fig. 6, p. 151). This phenomenon is apparently to 

 be explained on the supposition that subordinate thrusts traverse 

 the Silurian, like those affecting the passage-beds of Wallsgrove 

 Hill (pp. 172-73), where the beds nearest the thrust-plane tend 

 towards parallelism with it. 



XVIII. The probable Evolution of the West-of-England 

 Chain in several Sections not produced quite simultaneously. 



It has been pointed out (pp. 162-63) that the overfolds and over- 

 thrusts which have affected the southern end of the Abberley 

 liange took place before those which have elevated the bulk of the 



1 ' Geol. of Wyre Forest Coalfield ' Kidderminster, 1895, pp. 34, 36. 



