572 Geological Society. 



epicentre, and several elvan-courses — are all parallel to the isoseismal 

 axes, or nearly so. Besides the focal transference along the strike 

 of the fault-surface, the double series of vibrations gives evidence of 

 transference down the hade of the fault- surface, the focus of the 

 earlier shock being at a higher level than that of the second. 



2. ' On the Geological Structure of Portions of the Malvern and 

 Abberley Hills.' By Prof. T. T. Groom, M.A., D.Sc, F.G.8. 



This paper is in continuation of one on the Southern part of the 

 Malvern Hills already published by the Geological Society. In it 

 descriptions are given of the exposed rocks of theMalvern Range 

 from Swinyard Hill to North Hill, the district of Cowleigh Park, 

 Martley, Woodbury, Wallsgrove, and the neighbouring tract of 

 Goal Measures. The Silurian rocks west of the hills are almost 

 invariably inverted, and the Malvcrnian rock frequently can be 

 found to be overthrust on to them. In several cases there is 

 reason to suspect that slips of Silurian rocks are caught in infolds 

 among the Malvernian rocks. The author concludes that the 

 whole of this district, May Hill, the Old Red Sandstone tract to the 

 west, the coalfields of the Forest of Dean, South Wales, and Bristol, 

 and the Tortworth district, are traversed by a series of related folds, 

 whose axes run in two chief directions intersecting at a considerable 

 angle : the axial planes of one set tend to dip eastward, and of the 

 other in a southerly direction. Overfolding has taken place frequently 

 from the east, less frequently from the south ; and this inversion 

 affecis the south as well as the middle and north of the Malvern 

 range. The Archaean rocks are thrust on to various members of the 

 Cambrian System in the south and of the Silurian System in 

 the north. The overthrusts are more closely connected with a 

 later movement than with the first folding of the rocks, and while 

 they have not materially altered the nature of the rocks concerned, 

 they have in some cases resulted in the production of schists 

 (mylonites). In some cases a secondary folding has affected the 

 thrust-planes. The intensity of the folding diminished west of the 

 old ranges. The chief movement appears to have progressed in 

 sections from north to south, and the western fronts of different 

 sections show some tendency towards convexity in the direction of 

 movement. While the rocks affected by great movement range 

 from the Archaean to the Lower Coal Measures, the Upper Coal 

 Measures and Permian rest relatively undisturbed on the denuded 

 rocks of the range : thus the range is a member of the Hercynian 

 system produced during Coal Measure time, and probably the two 

 approximately rectangular directions of movement were practically 

 contemporaneous and were produced during the limited interval 

 between the deposition of the Lower and Upper Coal Measures. 

 There is no evidence to prove that the Malvern and Abberley Hills 

 formed part of a coast-line against which the Triassic beds were 

 deposited; for the Upper Bunter Sandstone forms the base of the 

 Trias throughout the district and rests unconformably on the Haffield 

 Breccia, together with which it passed unconformably over the site 

 of the West of I ngland Chain. The \,\ c sent position of the Permian 

 and Trias on the east of the hills is due to a post-Liassic fault of 

 moderate downthrow, which tends to run parallel to the western 

 front of the old range. 



