574 TKANS ACTIONS OF SECTION C. 



molar movements. The part which may be played by earthquakes in displacing 

 the earth's axis will depend upon the position of their origins, their frequency, and 

 the mao-nitude of the mass moved. A variety of observations have been made 

 which show that a megaseismic displacement is probably very much larger than 

 is usually supposed. A maximum quantity is given at ten million cubic miles moved 

 vertically through a distance of 10 feet. Even if we divide these figures by 

 twenty the molar movements are very large, and these are repeated on the average 

 every week. The cumulative effects of these, unless they are symmetrically dis- 

 tributed in latitude and with regard to the earth's axis, must be very great. 



2. Discussion on the Origin of the Trias. 

 (i) By Professor T..G. Bonney, Sc.D., LL.D., F.K.S. 



The three subdivisions of the Bunter, east and west of the Pennine Range, 

 apparently unite to the south of it, and thin out as they approach the southern 

 parts of Warwickshire, Staffordshire, and Leicestershire. In Devonshire it thins 

 out in a similar wedge-like manner towards the north and north-east, not reach- 

 ing the Bristol Channel. The upper and lower members in the northern area 

 are sandstones, generally red, often conspicuously current-bedded, but without 

 pebbles, the grains being frequently wind-worn. The pebble-bed reaches a thick- 

 ness of 1,000 feet near Liverpool — where, however, sand dominates over pebbles, 

 is about 300 feet thick in the northern part of Staffordshire, and rather overlaps 

 the lower sandstone. The author described the lithological characters of the 

 pebbles, and discussed the reasons for and against deriving them either from a 

 southern or south-western source, like those in the Devon area, or from any 

 region, either exposed or buried, in their more immediate neighbourhood, main- 

 taining a northern origin to be the more probable. The Keuper group, both 

 sandstones and marls, extends without interruption (except for the sea) from 

 Devonshire to beyond Yorkshire on the one hand and to Antrim on the other. 



The author considers the Bunter to be a fluviatile rather than a lacustrine 

 deposit, chiefly formed by large rivers. Two of these flowed from a mountain 

 region, of which Scotland and the extreme north of Ireland are fragments, and 

 a third from a similar region to the south-west of Britain. Deposits comparable 

 with the Bunter, and especially the pebble-bed, may be found on the border ot 

 the Alps, and these rivers probably traversed (at any rate early and late in the 

 Bunter epoch) arid lowlands, from which, if not absorbed, they may have 

 escaped by some channel now buried under south-eastern England. The Keuper 

 sandstones, as he showed, indicate the setting in of inland sea-conditions, the Red 

 Marls being generally regarded as deposited in a great salt lake. These, like the 

 clays of the Jurassic system, were probably derived from the mountain ranges, 

 which had previously supplied sand and pebbles. 



In fact, the physical and climatal conditions of the Trias — and the same 

 perhaps may also be said of the Permian — were probably to some extent comparable 

 with those now existing in certain of the more central parts of Asia, such as 

 Persia or Turkestan, 



(ii) By J. LoMAS. 



In order to test the opinion that the Triassic rocks of Britain have largely been 

 deposited under desert conditions, the chief characters and activities of existing 

 deserts were summarised. No deserts are free from water-action, and they may 

 exist with a comparatively large rainfall, provided it falls in a limited time and is 

 rapidly shed, and not stored up by glaciers, soils, or lakes. 



Thus the streams are mostly pluvial, and only occupy their channels temporarily. 

 Blown sand may fill the channels, cover the river gravels, and obliterate all surface 

 traces. Deposits are thus formed, consisting mainly of blown sand with lenticular 

 patches of gravel at various horizons. 



