ON THE EARTHQUAKE AND VOLCANIC PHENOMENA OF JAPAN. 89 



coloured clay rock, are visible as cliffs from 50 to 80 feet in height. In 

 Tokio, however, they only crop out at one or two places at the bottom 

 of deep cuttings. The depressions in the section represent the flood 

 plains of rivers which are tilled with soft alluvium. 



Rather than working on strata which had been so far crushed and 

 crumpled that further yielding is hardly to be expected, I should have 

 preferred a site yn the strata which are gently folded, and where a 

 measurable amount of yielding may yet be in operation. 



Although I had the choice of several caves as Kamakura, all of them 

 •were situated at some distance from the railway. To go and return from 

 the one I selected took six hours, and it was therefore seldom that it was 

 visited more than once a week. Very fortunately I received assistance 

 from Mr. P. E. Heerman, a gentleman who happened to be staying in the 

 neighbourhood, while one of tJie officials from the railway station kept the 

 lamps burning, and three times a day took readings of the instruments. 

 That the latter was attended to regularly was shown by a slight change in 

 the intensity of the photographic trace at the times when the lamps were 

 adjusted, a gap when they wei-e removed to be refilled and a slight notch 

 in the diagram from a self-recording tliermometer at the times when the 

 doors of the cave were opened, and the times at which these various marks 

 were made coincided with the times at which the readings were noted as 

 having been made. 



The cave seems to have been excavated on the line of a fault which, 

 curiously enough, is with difficulty recognisable on the face of the cliff 

 itself, but which is quite apparent in a photograph. The entrance to the 

 cave, which faces S.E., was, with the exception of the door, blocked up 

 with a wooden wall faced on the outside with a bank of earth and rubble 

 ■work 4 feet in thickness. The dimensions of the cave were 20 feet by 

 20 feet, with a heiglit cf from 7 to 10 feet. One corner of this was 

 partitioned off with wooden walls to form a room 10 feet square, and 

 from this the debris was cleared out to reach the solid rock on which two 

 brick platforms were built. 



These were one brick thick and laid with pure cement. On the end 

 of each of these platforms, which were at right angles to each other — one 

 running N.W. and the other N.E. — a small pillar three bricks high and 

 one brick square was built and capped with a slab of mai'ble. These 

 were finished on January 7, and the cave was left open for one week to 

 facilitate the drying. At the end of that time, on January 14, as the 

 cement appeared to have set, the instruments were placed on the slabs 

 and the records commenced. From that date, with but few interruptions 

 continuous photographic traces were obtained until March 18. These 

 machines I have called C and D. Machine C recorded tilting parallel to 

 the strike, while D recorded movements parallel to the dip. By a lifting 

 on the S.E. side the readings of the index attached to C increased in value, 

 while the readings of D increased with a lifting on the S,W. side. 



At the end of each week, when a photographic film was renewed, the 

 sensitiveness of the instrument was determined, after which it was re- 

 adjusted. These determinations are given in the following table. The 

 ratio of unity to the numbers in the first two columns is the tangent of the 

 angle through whicli tlie instrument would have to be tilted to 23roduce 

 a deflection on the photographic trace of one millimetre ; the corresponding 

 angles in seconds of arc are given in the third and fourth columns. At 

 the commencement it will be obsei'ved that to produce a deflection of one 



