ON SEISMOLOGICAL INVESTIGATION. 119 



VII. An atUmpt to detect and measure any relative movement of the strata 

 that may be noiv talcing place at the Ridgeway Faidt near Upivay, 

 Dorsetshire. — Preliminary Report by Horace Darwin, August 1900. 



The Fault for this experiment was selected by Mr. Clement Reid, and 

 is described by him in a separate report. It would have been better if 

 the rock had been harder and more impervious to water ; the solubility 

 of the carbonate of lime in the rock is also a disadvantage. The site is 

 easy of access, an essential point in such an experiment ; this, together 

 with the advantages pointed out by Mr. C. Reid, justify the selection of 

 the Fault. 



The Fault where the apparatus is fixed is a few yards east of the 

 Roman road and about 560 yards north of the cross roads in the village 

 of Upway, Dorsetshire, and is about 360 feet above Ordnance datum. 

 Gonville and Caius College, Cambridge, allowed the apparatus to be fixed 

 on their property and did all in their power to make the experiment 

 successful, and the Committee are most grateful to them. I must thank 

 Mr. Nelson Richardson for the many hours' help he gave me at Upway, 

 and in arranging for the experiment, and for the readings he took after- 

 wards. Thanks are also due to Mr. Loveless, the tenant of the land, 

 for the care he has taken in carrying out the work and the help he gave 

 in every way. 



Four positions were taken in a straight line approximately at right 

 angles to the fault ; these positions will be denoted by the letters N.N., N., 

 S., S.S. ; N.N. is 9 metres and N. 4^ metres north of the Fault, and S.S. 

 is 9 metres and S. 4^ metres south of it. The apparatus is arranged to 

 measure the relative vertical movement of the strata at these four 

 stations. There are advantages in selecting four instead of two stations. 

 If there had been only two stations, and the apparatus got damaged at 

 one of them, the experiment must have been a failure ; also, if there had 

 been any accidental displacement of the apparatus relatively to the strata 

 at either of the two stations it might have led to misleading results. 

 With four stations such damage or movement will probably be detected, 

 and the results, though less valuable, will not be rendered quite useless, 

 as would be the case with only two stations. 



The movement of the strata at the Fault may take place in any or all 

 of the following ways : — 



(1) The strata on both sides of the Fault may tilt as a whole without 

 any slip taking place at the Fault. 



(2) The strata at the north side may tilt and the south side not tilt, 

 and still no slip at the Fault. 



(3) The strata at the south side may tilt and the north side not tilt, 

 and still no slip at the Fault. 



(4) There may be slipping at the Fault with no tilting. 



These four movements may be all taking place at the same time, and 

 the use of four stations will allow of each movement being separated from 

 the others. 



The apparatus has been designed by me and made by the Cambridge 

 Scientific Instrument Company, Limited. I have not been able to give 

 sufficient time this summer to overcome some difficulties which I regret 

 that I did not foresee, and it is for this reason that no numerical results 



