On Some Geological Aspects of the East Anglian Earth-Quake of April

20 11. HICKS ON BONE-CAVES IN WALES. that the borders of the Bristol Channel, where the caverns mainly occur were but little affected at the time in comparison with such an area as the Vale of Clwyd, in the immediate neighbourhood of a mountainous district with great glaciers, opening also to the north and therefore subject during the period of submersion to the influence of floating ice from more northern areas. ORDINARY MEETING. FRIDAY, DECEMBER 5TH, 1884. HENRY HICKS, ESQ., M.D., F.G.S., President, in the chair. The list of donations to the library since the last meeting was read, and the thanks of the Association were returned to the donors. The following were elected members of the Association :-J. Alston; R. B. Grantham; T. D. Palmer Jones j H. Lawrence j A. G. Leeson j W. Mawer, F.G.S.; H. L. Millar. The following paper was then read: _If Preliminary Notice of the East Anglian Earthquake of April 22nd, 1884." By Raphael Meldola, Esq., F.R.A.S., F.C.S. ON SOllE GEOLOGICAL ASPECTS OF THE EAST ANGLIAN EARTH QUAKE OF APRIJ, 22ND, 1884. By RAPHAEL MELDOLA, F.R.A.S., F.C.S., &c. Rarely in the history of British earthquakes has a shock been experienced of such destructiveness as that which I now propose to bring under the notice of the Members of the Geologists' Asso ciation. Among the most noteworthy of these visitations during the period extending from the 12th century down to the present time, we have but about half-a-dozen records which as regards structural danger can be compared with the present disturbance. In 1185 Lincoln Cathedral and many other buildings in the county were seriously damaged. In 1248 a violent shock in the west of Eng land caused the partial destruction of the Cathedrals of Wells and St. David's and many other churches in Somersetshire were damaged. In 1275 again many churches are said to have been damaged in the western counties, and St. Michael's, Glastonbury, thrown down. In 1382, the sixth year of Richard II., many OEOLoolcAL ASP~CTS OF THE EAST ANOLIAN EARTHQUAKE. 21 churches in the south-east of Eugland are reported to have been thrown down. In 1480, buildings were thrown down by a violent earthquake having its focus in the eastern counties. In 1580 a strong shock in Kent and Middlesex damaged old St. Paul's and the Temple Church and threw down many chimneys in London. In 1750 structural damage was again caused in London, and later in the year another shock threw down chimneys in Northampton. In 1786 some destruction was caused by an earth quake which visited the north and north-western counties and extended into Scotland, the Isle of Man, and Ireland. The present disturbance appears to have originated about 9.18 a.m. on April 22nd, beneath the earth in the neighbourhood of the little villages of Abberton and Peldon in Essex, between Colchester and Mersea Island. Immediately after the occurrence I commenced to collect information, being fully alive to the necessity of not allowing such a visitation to pass without bcing, in the interests of science, as far as possible exhaustively reported upon. The estab lishment in the county comprising the seismic centre of a well known and energetic local society, having members scattered throughout the various parts of Essex, promised to afford unusual facilities for the preparation of such a report, and the Essex Field Club, as the nearest organized scientific body, appeared to me to be the proper central authority for undertaking the investigation. On behalf of this society I took upon myself the labour of draw ing up the report, although not without certain misgivings, as I was aware that my own pursuits in other fields had not hitherto led me to the serious consideration of seismological problems, and above all I felt that the demands upon my time would leave me with but little leisure to pursue my task uninterruptedly. Since April, however, I have been steadily carrying on the work, 'and the report is now in a state approaching completion. The necessary slowness of the work, due in part to the delay ill receiving the large amount of scattered evidence from the various parts of Eng land, has prevented any statement of results up to the present time, and although some of these results have in consequence been to a certain extent forestalled by other observers, I have thought it advisable to reserve publication until the history of the East Anglian earthquake can be presented to the scientific and general public as a connected whole. Taking the earliest opportunity of visiting the area of destruc tion, accompanied by my friends Mr. T. V. Holmes, F.G.S., (late 22 n. MELDOLA ON SOME GEOLOGICAL ARPECTS OF of H.M. Geological Survey), and Mr. William Cole, lIon. Sec. of the Essex Field Club, I left for Colchester on May 3rd, and made [\ detailed inspection of all those places where the damage had bcen greatest. This visit was much facilitated by the attentions we re ceived at Colchester from Mr. Henry Laver, F.L.S., and Mr. J. C. Shenstolle, F.R.:VLS. On May 10th, at the invitation of the Mayor of Maldon, I visited that town in order to address a mect ing on behalf of thc Mansion Honse Relicf Fund, and through the kindness of my friend Mr. E. A. Fitch, F .1,.8., I was enabled to collect further information. On August 4th, a meeting of the Essex Field Club was held in the earthquake district, and although most of the damaged buildings had by that time been repaired, a few additional observations were made. Before our first visit to the scene of damage, I learnt that my friend Mr. G. J. Symons, F.R.S., had already been over the ground, and an interview with that well-known meteorologist for tunately secured his hearty co-operation. Mr. Symons had written to the Times tbe day after the shock, asking for information, and during his inspection had marked all the cases of damage that came under his observation on the 6-incb Ordnance map, and had also made many notes in tbe field. After publishing an abstract account of the earthquake in the May number of the 'Meteorological Magazine,' Mr. Symons was good enough to hand over to me the whole of his correspondence, notes and maps, and whilst expressing my thanks for this courtesy I will take the present opportunity of stating that tho completeness of the re cords is largely due to the assistance which I have from the first received from him. Want of space forbids me here from thanking in detail my own numerous correspondents, and I will only state that by means of direct application and a set of questions most kindly circulated through the local papers I have received many hundred letters from Essex and other parts of England. It is impossible also to mention here individually the names of all those from whom I have received assistance of various kinds, but I mnst state that my labours have been considerably facilitated by the co-operation of my friend, Mr. William White, who kindly under took for me much of the correspondence, and who is now assisting we in drawing up a complete preliminary catalogue of British Earthquakes. I must not omit to add that Mr. J. C. Shenstone, of Colchester, TilE EAST A~GI.L\N EARTHQUAKE. 23 has afforded me much valuable local-aid, and I have great pleasure also in acknowledging my indebtedness to the local press, the excellent, and, on the whole, rcmarkably accurate accounts having been of the greatest service in drawing up the report. The intensity of the present disturbance will be best learned by examining the area over which the shock was felt. Taking Abberton as the centre, the extreme distances are Brigg (Lincoln shire), 135 miles north-north-west; Altrincham (Cheshire), 180 miles north-west; Street (Somersetshire), 170 miles west-south west; Freshwater (Isle of Wight), 135 miles south-west; Bon logne, 90 miles south-south-east; and Ostend, 100 miles south-east. A parallelogram drawn through these stations would be 242 miles east and west, and 200 miles north and south, giving an area of 48,400 square miles. In round numbers the shock may he said to have entended over nearly 50,000 square miles. An approximate comparison of the intensity of the present shock with that of other well-known earthquakes is given by the ratio between the squares of the radii of the disturbed areas. This follows according to Prof. Milne." from the circumstance that the quantity of material shaken being as the square of the radius of thc disturbed area, and taking the quantity of material moved as proportional to the moving force, the intensity of tho shock varies as the square of the radius, assuming that the shock originates at the same depth beneath the two areas being compared. Thus the mean radius of the present earthquake is about 135 miles, and that of the great Lisbon earthquake of 1755 was 600 miles. The relative intensities are therefore :- 6002 : 1352 = 360,000 : 18,225. The East Anglian disturbance, according to this estimate, was a little over one-twentieth the iutensity of the Lisbon earthquake, but this result is possibly too high, owing to the exaggeration of the radius by the conduction of the shock along the older rocks, as will be explained subsequently. The area of structural damage comprised 50 or 60 square miles, the main axis of disturbance extending for about five miles in a north east and south-west direction between Peldon and Wyvenhoe on the river Colne.

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