the former river gorge into the present magnificent "Golden Gate." So clearly had the geotectonic structure of the region been worked out by Lawson, that the speaker had ventured in a public address (within a fortnight of the occurrence of the earthquake) to offer with some confidence what seemed to him-as a deduction from Dr. Lawson's paper-to be the true explanation of the earthquake, in the sudden relief of strain in the bed-rocks of the region, along a plane or planes of slip-faulting, which are generally found in the synclinal portions of all great flexures of the earth's crust.

In the interim "Report" of the Commission, which reached him three or four weeks later from Dr. Lawson, he had the satisfaction to find that the explanation he had suggested agreed with that put forward by the Commission as given in Dr. Upham's paper.

The speaker regretted that Dr. Upham had not been able to give more detailed information, at present, as to the nature of the crustal movements, which had operated with such disastrous results in the Valparaiso region; but he strongly suspected that further investigations might result in interpreting those upward movements mentioned by the author, as indicating "over-thrust " fault-planes due to the fact that the region in question is situated on the ridge of an anti-clinal fold. If that should turn out to be the case, the fact would probably account for the wider extension of the disastrous results there than in the San Francisco region.

Dr. Irving ventured to put before the Meeting an interesting problem, which had presented itself to his mind, as to a possible connection in time between the occurrence of the San Francisco earthquake and the great eruption of Vesuvius about a week before, with the abnormally extensive extrusion of lava from the depths at which molten or potentially-liquid rock-material exists.* The latitude of Vesuvius and of San Francisco being nearly the same, and approximately 40° N., a simple calculation gives us a rapidity of rotational movement from west to east along that zone of latitude of something like 700 miles per hour (about ten times greater than the velocity of the fastest express train) to represent the 1,000 miles per hour velocity of rotation of the outer rind of the earth in equatorial regions. The extrusion of lava at Vesuvius

* On this point reference may be made to the speaker's letters to Nature in May, 1905, vol. lxxii, pp. 8 and 79.

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and the escape of vast quantities of super-heated water would tend to create a vacuum below the mountain; but that result would be prevented by the inflow of the surrounding molten or potentiallyliquid material. Taking into account the vast eastward momentum (here pointed out) of the whole mass, dynamical considerations led us to believe that the inflow would be chiefly from the west of the Neapolitan area; and therefore the power of buoying up the crust would be diminished along a zone of latitude extending a good way in that direction round the globe. Such a disturbance of equilibrium would make itself especially manifest where the conditions of the crust caused local weakness and a tendency to subsidence, such as Dr. Lawson had shown to exist in the San Francisco region. He put this forward as a thesis for discussion, and would be glad if any better mathematician than himself could find a flaw in the argument.

[It might be noted that the great San Andreas line of fault shown on the map accompanying the paper, running nearly parallel to the Coast Range, was also shown on a very valuable map, which had been constructed by Professor Branner, of Sandford University, and was published in the Supplement to The Times on December 17th, 1906, showing how seismic intensity was centered in and around the San Francisco region as the result of the local instability of the crust.]

Professor H. LANGHORNE ORCHARD, M.A., B.Sc.-Although tectonic earthquakes may be said to be independent of volcanic action, yet there is a connection between earthquakes and volcanoes. Volcanoes form outlets for the accumulated and pent-up energy, thus moderating the violence of the outbreak. The volcano is like the safety-valve of a steam-engine. This explains the fact (referred to by the author) that earthquakes accompanied by volcanic action are less destructive than others.

With regard to the two great seismic belts (traced out in the paper), it is a relief to note that England is not in either of these belts, though apparently perilously near to the second. Probably we owe more than is generally supposed to the friendly vicinity of Iceland.

The great depth of rupture, in the case of the San Francisco earthquake, is remarkable, and the Investigation Commission are to be thanked for directing attention to the importance, in relation to geophysical science, of studying the question of depth.

I should like to ask Professor Hull what, in his view, is the general explanation of the circumstance that earthquake waves which are propagated through loose geological formations are more disastrous than those propagated through firm ones as stated by the author.

We shall concur with the learned author that these destructive visitations afford no argument against the goodness of God and His over-ruling power; and that it is death itself, not its method or mode, that claims our serious concern. Undoubtedly, the only sure basis for a rational fortitude in presence of death is that unlimited trust in God which was possessed by Job.

Professor LOGAN LOBLEY, F.G.S.-Besides being an interesting account, Dr. Warren Upham's paper contains some points of considerable scientific and seismic value. With its main contention that the two earthquakes were of tectonic and not of volcanic origin I am in entire agreement.

Such earthquakes are the result of forces originating pressures, strains and tensions which, when resistance is overcome produce, a sudden movement of the surface rocks. The whole of the Pacific coast of America is being elevated, and it is this that causes its frequent and sometimes disastrous earthquakes, as well as the volcanic activity which is also a conspicuous characteristic of this region. Thus both the earthquakes and the volcanic eruptions have the same ultimate cause and so are, in a sense, related.

I cannot, however, agree with the author that these forces are produced by the shrinkage of the globe from cooling, for I have shown, I think, conclusively, that there has been no appreciable diminution of the mean radius of the globe since Cambrian times. These great forces producing elevations and subsidences, rock foldings and earthquakes, and giving the conditions allowing volcanic action are, I believe, due to regional expansions and contractions.

Neither can I favour the suggestion that there was a connection between either of these seismic movements and an eruption of Vesuvius ejecting an insignificant amount of material 6,000 miles distant.

We certainly owe our thanks to Dr. Warren Upham for presenting us with his concise account of two memorable catastrophes.

Col. T. H. HENDLEY, C.I.E.-Previous speakers, as well as the writer of the paper, have referred to the rapidity of the transmission of the earth tremors. Under certain circumstances the

motion may be seen, as for example, when, one night in the hot season, I was reading in bed in a large room in India, of which the floor was a smooth surface of white marble cement. A smart earthquake shock occurred, and my bed was actually raised, but the solid floor, nearly six feet thick, heaved up like the sea when a wave passes over it, without being broken.

Dr. Upham observes that the intensity varied greatly over the large disturbed area. Even in small districts such variation is noticed.

In Mymensingh, in Eastern Bengal, I saw the ruins of the English church, which was represented by a pile of stones. Houses close by were also destroyed, yet within a few yards of them stood others which were intact.

The curious effects of earthquakes were peculiarly illustrated in Bengal, where I would mention the case of a temple spire near the Dacca Racecourse. The upper part of the heavy solid shaft had been separated by a horizontal fracture from the lower portion, and had been turned round, without leaving the perpendicular, so as to rest at an angle upon its base. Many other peculiar effects are often noticed, such as distortions of rails, extraordinary alterations in positions of the parts of walls, and so on.

As to the moral and mental effects glanced at by Dr. Upham, the Nawab of Murshidabad, being an invalid, was carried out of his palace by his servants when the great Bengal earthquake took place, and although he himself escaped, the severe injury and death to one of his men so affected him that at the time of my visit he would never remain long under a masonry roof, but received his friends in a small thatched building. Similar instances are very

common.

As regards the great destruction attending sea waves which are raised by submarine shocks, we might instance the enormous loss of life some years ago, amounting to perhaps a quarter of a million persons, in the Bakarganj disaster in the Sundarbans in the Ganges Delta. Even an ordinary rise of a foot or two at flood times in the monsoon season is dangerous. Once when I was going in a steamer towards Barisal the capital of that district, I saw cattle on a village site standing with their heads just out of the water, and villagers on the house roofs, all waiting patiently for the flood to subside. It is easy under such conditions to realise

what a sudden upheaval and a great sea wave may do. When the great disaster of which I have spoken happened, many feeble persons escaped only because they were not strong enough to get away in boats or retreat to higher ground and were left in the tree tops.

There are many other incidental questions which are suggested in the interesting paper to which we have listened, but I would only ask one question, and that is, whether any observations had been made as to the effect of the San Francisco earthquake on the barometer? When the Krakatoa catastrophe occurred the meteorograph at Jeypore, which was under my care, indicated that a wave passed round the world two or three times.

Professor HULL, F.R.S. (Secretary)—I wish, in seconding the resolution, to be allowed to make a few remarks on the geological aspects of this valuable communication.

First I may observe that this earthquake shock of 1906though lamentably disastrous to life and property-if it had taken place two centuries ago, would have been passed over as a matter of indifference to the outer world.* If there were any inhabitants at

all, they would have consisted of a few Indians, to whom the shock would have brought no great terror or loss. The disasters which followed the earthshock of last year were due to the existence of a great city with all the appliances of modern civilisation.

Second-The vertical displacement of the ground and rocks on either side of the St. Andreas fault, or fissure, was trifling when compared with that which has taken place in very recent geological times in other parts of the world. For instance, the great fault crossing the Grindelwald in Switzerland, which I have myself seen, along which the granitoid rocks are upheaved several thousands of feet, is as recent as the Middle Tertiary or Pliocene period. That of the Arabah Valley in Arabia Petræa, which has been traced for about 400 miles from the Gulf of Akabah into Syria, has an uplift of about 4,000 feet where it passes along the eastern margin of the Dead Sea and is of the same age; and, to come nearer home, the fault which bounds the great plain of Cheshire on the east side at the foot of Mowcop, in North Staffordshire, has a displacement of about 3,000 feet. But what is remarkable is, that the two former

* San Francisco was not occupied by Europeans till the year 1776.