August 2, 1883] 



NA TURE 



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through a pressure which the earth's crust is not rigid 

 enough to resist, and that so long as this pressure is 

 sustained they must remain at least stationary. There is 

 no proof anywhere that the pressure that caused the ele- 

 vation is now removed, but there are frequently indica- 

 tions, such as earthquakes and landslips in mountain 

 chains, that it exists and is even on the increase. On the 

 other hand, there is no evidence of any kind to show that 

 some, especially of the older mountain chains, ate not 

 sinking, though subsidence in such cases would be very 

 difficult to detect. Besides this it is conceivable that 

 when the force w hich has squeezed the crust into folds has 

 ceased to be exerted it is not flexible enough to regain 

 its original horizontal position, but will remain in folds, 

 and as there is no increased thickness, and consequently 

 no addition of weight, but on the contrary a continual loss 

 from denudation, there is no reason why they should not 

 retain their position upon the hypothesis of a continuous 

 molten layer subjected to greatest pressure at its lowest 

 levels. Dr. Fisher even assumes that the mere removal 

 of weight from them by denudation, and its accumulation 

 on their flanks, would suffice to cause a continuous up- 

 heaval. The deflection of the plumbline has shown that 

 the density of the crust beneath mountains must be less 

 than that below the plains, and the relatively slow rate at 

 which heat increases in boring through them shows also 

 that the pressure there cannot be so great. Though 

 strata are compressed into a smaller area through the 

 folding, it is doubtful whether the aggregrate pressure on 

 the liquid layer in such regions is at all increased, while 

 in elevated plains it obviously cannot be so, as there is in 

 that case no direct increase of weight. It thus seems as 

 if it were as necessary that the crust of the earth should 

 yield to increasing pressure as that the sea should roughen 

 under the wind, and the apparently arbitrary upheavals 

 ar d depressions are brought under a definite law. The 

 greatest depths of the ocean would ever deepen and its 

 superficial area tend to diminish, while that of the dry 

 land would increase, and its mountain chains reach higher 

 elevations. The theory appears in harmony with the 

 truths of geology and of astronomy, for the records of 

 Palaeozoic times show neither evidence of great depth of 

 sea nor mountainous elevation on land, the organic 

 remains pointing to a little varied surface. The highest 

 mountains are geologically the most recent, and evidence 

 of deep seas increase towards the Cretaceous period, 

 while our satellite, whose evolution may have progressed 

 more quickly than ours, has relatively far greater, more 

 numerous, and more abrupt elevations than the earth. 



Somewhat similar conclusions to these have been 

 arrived at in the " Physics of the Earth's Crust," by Dr. 

 Fisher. Without presuming to compare the present 

 superficial treatment of the subject with that great and 

 philosophical work, some important differences will be 

 observed between the views there expressed and these, 

 as well as some entirely new observations and extensions 

 of the theory. The views advocated are still so far from 

 being generally accepted by geologists that their publica- 

 tion in Nature will doubtless put many in possession of 

 facts and inferences which are in a general way only 

 accessible to those who have leisure to gather them from 

 less popular publications. J. Starkie Gardner 



THE ISCHIA EARTHQUAKE 



ONE of the most disastrous earthquakes on record 

 occurred in the little Island of Ischia, in the Bay of 

 Naples, on the evening of July 28. It was only in March 

 1881 that a similar catastrophe occurred at the same place. 

 The island is a favourite summer resort of Romans and 

 Neapolitans, and Casamicciola, where the destruction 

 was greatest, was crowded with strangers. The full ex- 

 tent of the loss of life has not yet been ascertained ; but 

 up to the present it is estimated that at least 4000 have 



been killed, and very large numbers wounded. The 

 earthquake occurred at half-past nine, when strangers 

 and natives were enjoying themselves in various ways 

 under a cloudless sky with not a breath of air stirring. 

 Not the slightest warning seems to have preceded what 

 occurred ; in the space of fifteen seconds Casamicciola 

 was a heap of ruins, while a similar fate overtook the 

 smaller towns of Forio, Laco Armino, and Fontana 

 Serrata. At present we can only record the facts of the 

 case ; when further details are to hand it may be possible 

 to throw some light on the real cause of the catastrophe. 

 Besides the first shock, which lasted fifteen seconds, other 

 two were noticed immediately after. Prof. Palmieri is 

 stated to have expressed the opinion that the catastrophe 

 was caused by a sinking in of the level, and not by an 

 earthquake. On the 31st there was another slight shock; 

 while Vesuvius is in a state of active eruption. A Rhenish 

 journal states that on Saturday night, about the time 

 when the Ischia earthquake occurred, a tremendous 

 motion of the earth was distinctly felt at Wiesbaden. On 

 the morning of the 31st also, it may be noted here, a 

 shock of earthquake was felt in Uporto, lasting two 

 seconds, with direction east and west; it naturally caused 

 great consternation. Two shocks are reported to have 

 occurred on the same day at Gilroy, California. With 

 regard to the volcanic Monte Epomeo in the Island of 

 Ischia, we may say that its last recorded eruption took 

 place in 1302. 



We are glad to learn that Dr. Dohrn, director of the 

 Naples Zoological Station, who was in Ischia at the time, 

 escaped unhurt. 



THE AGRAM EARTHQUAKE x 



IN connection with the Ischia Earthquake, the official 

 repott of the Agram Earthquake of three years ago 

 may not be without interest. The detailed report by Herr 

 Hantken von Prudnik contains all the information which 

 he had been able to collect regarding the severe earth- 

 quake with which the district surrounding the town of 

 Agram in Croatia was visited on November 9, 1880. 

 Herr von Prudnik gives not only an exhaustive narrative 

 of his own observations of the effects of the earthquake, 

 made a few days after its occurrence, but also some 

 account of careful observations made by inhabitants of 

 the district where the earthquake actually took place ; and 

 his memoir is full of most interesting matter to seismo- 

 logists. The district is situated in an area within which 

 earthquakes are of very frequent occurrence, for Herr von 

 Prudnik gives a long list with descriptive notes and dates, 

 beginning with March 26, 1502, and coming down to 

 Nov. 9, 1880, but most of them within the present century, 

 of earthquake-shocks, some of which seem to have been 

 severe, which have been felt in the locality. A few self- 

 registering seismographs erected in suitable places in the 

 district would yield, we think, much valuable information 

 and would detect many of the smaller motions, partaking 

 rather of the nature of tremors, which are no doubt fre- 

 quent, but which, although of great seismological import- 

 ance, remain unnoticed where such appliances are not 

 in use. 



With regard to the earthquake of November 9 itself, 

 the shock seems to have been very severe, causing as it 

 did, besides loss of life, a vast amount of damage to 

 public and private buildings, especially churches. The 

 details of the damage done, given by Herr von Prudnik, 

 are very interesting, and illustrate very clearly the conclu- 

 sions which have already been arrived at by seismologists 

 as to the effects of the conformation of the ground in the 

 neighbourhood of a building, and of the structure of the 

 building itself, in diminishing or in aggravating the 



1 " Das Erdbeten von Agram in Jahre 1880." Bericht an das k. ung. 

 Minislerium fur Ackerbau. Industrie, und Handel, eingereicht von Max 

 Hantken von Prudnik. gewesenem Director der k. ung, geologischen Anstalt. 

 (London : Trtibner and Co., 1882.) 



