332 Bevieirs — Great Indian EartJi quake. 



three oi' four months in flooding the disturbed area with circulars, 

 though work of this kind had of course to be done. The materials 

 to be collected were not the fleeting impressions of a transitory 

 phenomenon ; they were for the most part permanent eff'ects that 

 could be examined without haste, suffering little from the lapse of 

 time and nothing at all from defects of the human mind. They had 

 to be observed, disentangled, and classified, — no light woi'k, rather 

 one requiring, and, what is more, obtaining, the best energies of 

 a capable field-geologist. 



It would not be easy within moderate limits to refer to all the 

 points of interest that are to be found in this report. Though filling 

 a complete volume of the Memoirs, and extending to more than 

 400 pages, it should be read from cover to cover, not by seismologists 

 alone, but by every geologist who wishes to study the mechanics of 

 mountain-building or to realize the scale on which the operations of 

 nature are sometimes carried out. In doing this, he will no doubt 

 be struck by some passages more than by others. Among them he 

 will probably include the descriptions of the fissures that were formed 

 in alluvial ground far away from river-banks, etc. (pp. 83-94), of 

 sand-vents and the forcing up of river-beds and the bottoms of wells 

 (pp. 99-107), and of the numerous landslips (pp. 111-123) ; the 

 chapter on the earthquake-sound and on Barisal guns (pp. 191-207) ; 

 the investigation of the velocity of the earth-wave within the 

 disturbed area (pp. 53-77), and the tracking of the unfelt vibrations 

 through the body of the earth and of the surface-undulations almost 

 completely round the globe (pp. 227-256). To the physicist the 

 last-named chapter will prove the most interesting ; but the geo- 

 logist will probably regard with the highest favour that which deals 

 with the permanent changes in the epicentral tract. Here we have 

 described the Chedrang fault-scarp (pp. 138-147), which crosses 

 many times the river of that name, forming a series of waterfalls 

 and lakelets along its course; the Bordwar fracture (pp. 148-151) ; 

 numerous pools, due to a reversal of drainage, but without any 

 visible connection with faulting (pp. 152-157) ; changes of level 

 evidenced by the visibility of rivers and roads formerly hidden by 

 intervening hills (pp. 157-163) ; and, in an appendix which properly 

 belongs to this chapter, an account of the re-survey of certain 

 trigonmnetrical stations within the epicentral area (pp. 361-371), 

 the chief result of which is to show the urgent need of its repetition 

 •on a much larger scale. 



Exceptional as the Indian earthquake was, one cannot I'ead without 

 astonishment of the vast district over which these permanent changes 

 took place. Mr. Oldham estimates that it was about 200 miles in 

 length, not less than 50 miles in breadth, and more than 6,000 

 square miles in area. The fault-scarps and fractures discovered 

 within it are merely evidences of displacements continued up to the 

 surface. The}' manifest the extreme complexity of the earthquake's 

 origin, which Mr. Oldham traces to a slide along a huge, but hidden, 

 thrust-plane, inevitably accompanied by nearly simultaneous and 

 more or less visible movements along the minor faults connected 

 with it. 



