478 



SCIENTIFIC NEWS. 



[Nov. 9, 1888. 



to view, running parallel with the others, but of much 

 greater solidity, being nearly 4 feet thick, and built of 

 stones and mortar. Fragments of pottery, including some 

 Samian (?) ware, were frequently dug up, and among 

 the debris a piece of a bronze fibula. Another 70 feet 

 brought the trench to another wall of stone and mortar, 

 only 2 feet thick, and not running right across the trench ; 

 further investigation brought an angle of this wall to 

 light, and it was almost certain that some enclosed space 

 had now been entered. The excavations from this point 

 teemed with interest. The trench passed over the wall 

 forming the angle, as noted above (being evidently the 

 wall of an enclosed space), exposing 27 feet of it, when 

 another wall at right angles to it was met with, and thus 

 introduced a second enclosed space. In the first enclosed 

 space part of a quern, or hand-mill, was dug up, whilst 

 the small corner of the second enclosed space, included 

 in the area cut by the trench, proved to have plastered 

 and decorated walls as well as a tesselated floor ; more- 

 over, human remains were exhumed here. 

 (To be continued.) 



SUBMARINE EARTHQUAKES AND 

 ERUPTIONS. 



"C^REQUENTLY and closely, as it is remarked in the 

 Naturforscher, as the quakings of the dry land have 

 been investigated concerning the manner of their occur- 

 rence, their extension, and their causes, exceedingly little 

 is known concerning the quakes of the sub-oceanic por- 

 tion of the earth's crust. Nothing has been ascertained 

 and recorded beyond the bare fact of their existence. 

 At most we may say that the so-called earthquake tidal 

 waves, such as those of Simoda (1854), Arica (1868), 

 and Iquique (1877), have given occasion to researches. 

 But the object in view was not so much to ascertain the 

 causes of the phenomena as to draw from the move- 

 ment of the waves conclusions as to the depth of the 

 ocean. Recognising this deficiency in our knowledge of 

 the seismic action of the earth's crust, Herr E. Rudolph, 

 of Strassburg, has undertaken to collect all accessible 

 records of seaquakes in a catalogue which extends to 

 eighty pages. He characterises and classifies the sea- 

 quakes in accordance with the variable manner of their 

 occurrence and their mechanical action, and explains the 

 processes on the basis of the physical laws of wave- 

 motion in solids and liquids. 



This author gives the name of seaquakes to all agita- 

 tions which have their origin in the bottom of the sea, 

 and which, passing over to the mass of the ocean, are 

 propagated as waves of elasticity. They are manifested 

 to the observer by the shock which the ship undergoes, 

 by a noise, and by phenomena on the surface of the 

 sea. 



A seaquake is felt by the sailors as if the ship had 

 run aground, and was passing over it rapidly. According 

 to the intensity of the shock, it may be merely a gentle 

 but strange trembling in the ship, but in stronger shocks 

 heavy objects are overturned, men are flung upwards, 

 and ships even dismasted. In extreme cases the vessel 

 itself may be lifted or thrown on its side, though its direc- 

 tion and speed are unaffected. As to the nature of the 

 shock, both undulatory and succussory movements can 

 be felt. 



The atmosphere is not affected in seaquakes, save" that 

 there "occur phenomena of sound which seem to have 



their origin in the sea, and which have been compared 

 to a rumbling, or to distant thunder. 



According to the action of seaquakes upon the water 

 they are divided into two great classes. In the majority 

 of cases the submarine shock passes over without exert- 

 ing the least influence upon the mass of water. A 

 change in the condition of the sea is not produced by 

 the most intense shock in perfectly calm weather. This 

 holds good alike in deep and shallow water, even along 

 coasts. In some cases an ebullition was observed, and 

 peculiar jets of water, like those produced by the impact 

 and rebound of violent rain, were thrown up to the 

 height of about fifteen inches. 



From such seaquakes Herr Rudolph distinguishes those 

 which raise up the water in mighty waves in all direc- 

 tions. At the same time the sea throws up abundance 

 of bubbles, a roaring sound is heard in the depth, vapours 

 are given off, and the water becomes distinctly hot. 



As to the duration of these seismic movements under 

 the sea, the extent and the limits of the region shaken, 

 and the speed of the propagation of the shock, little can 

 be said, as, for the most part, each seaquake is recorded 

 by one ship only. Often many shocks succeed each other 

 at brief intervals, but the duration of each shock is for 

 the most part very short, and prolonged agitations are 

 rare. An extensive region has been observed to be 

 shaken in four cases only. The rate of propagation on 

 the surface from the epicentrum was found to be 594 

 metres in a great seaquake in the Bay of Bengal. 



The author attempts to explain the phenomena ob- 

 served by a comparison with those produced in submarine 

 blasting operations undertaken to remove a sunken rock 

 in the harbour of San Francisco, and reported by the 

 younger Le Conte in 1874. In this manner he very suc- 

 cessfully refers the ordinary seaquakes, in which the 

 surface of the sea is not disturbed, to submarine shocks. 

 Those cases when huge waves are raised which dash 

 upon the coasts in the manner of an exaggerated flood- 

 tide are the result of volcanic outbreaks beneath the sea. 



Seaquakes have been experienced in all seas, deep or 

 shallow, and in their distribution they do not depend on 

 the plasticity of the bottom. There are, however, certain 

 regions in which they are exceptionally frequent, as in 

 the Atlantic, in the seismic zone of St. Paul's Rocks and 

 on their eastern side, near the Azores and the Lesser 

 Antilles, near the Sunda Islands in the Indian Ocean, and 

 along the greater part of the coasts of the Pacific. The 

 " earthquake flood-waves " are almost peculiar to the 

 Pacific coasts. 



Rudolph forms the conclusion that the frequency and 

 intensity of the manifestation of seismic and volcanic 

 forces at the bottom of the sea is not connected with the 

 distance from active or extinct volcanoes on the dry 

 land. 



If we except the few regions which are quite free trom 

 seaquakes, the bed of the ocean is, as compared with the 

 land, a region of intensified seismic and volcanic activity. 



Lastly, the author inquires into the causes of seaquakes. 

 In four cases he shows a probable connection of seaquakes 

 with dislocatory fractures, and two of these cases were 

 accompanied by submarine eruptions. The numerous 

 seaquakes of littoral zones he refers also to similar 

 fractures. The desultory seaquakes occurring in all 

 oceans, and especially in the deeper regions, are con- 

 sidered to be shocks produced by the injection of molten 

 matter into the plastic substance of the deeper parts of 

 the earth's crust. • - -- - - ....... 



