Jan. 31, 1889] 



NATURE 



331 



out adding in any way to thrse views. Chapter ii. is a revisw 

 of the earthquake parts of Italy referred to in the report, 

 together with an attempt to separate the country into seismic 

 provinces, a worlc aheady in part carried out by Mercalli, and 

 where observatories are wanting to suggest the establishment of 

 ihem. Apjiended to tliis memoir is a map of Italy coloured in 

 nine tints, showing the seismic intensity in different regions. If 

 the reader compare this with a geological map of the country, he 

 will be struck with the relationship of earth-movemtnts and the 

 rocks. We notice intense foci near Sienna, north of Florence, 

 and the alluvial fiats of the mouths of the Po, another in 

 Umbfia, and .t very intense one between Aquila and Solmona, 

 where the Apennines reach their greatest elevation. There are 

 the two volcanic centres of Naples and Melfi, with the interven- 

 ing of BerteVento and Ariano, a district in which comparatively 

 recent rocks are much metamorphosed, whilst to the south-west of 

 Totenza we observe a large but only moderately intense focal 

 area. The toe of the Italian boot looks very dark with the two 

 intense centres of Cosenza and Aspromonte, together with the 

 ■Mesfina ci=;tiict in Sicily. In these we have granite, gneiss, 

 ami other crystalline rocks, covered chiefly by more or less friable 

 Tertiary doixtsits, much eroded into many narrow deep valleys, 

 and sharp crumbling intervening ridges. One cannot but be 

 struck" by the striking relationship between the distribution of 

 seismic areas and the alluvial flats, the volcanic regions and more 

 active points of mountain-building in the geologically-speaking 

 young country of Ita'y. In fact, this map constitutes the most I 

 important part of the report. ' 



The last two memoirs are descriptive in character, dealing with 

 the two recent destructive earthquakes. Of these two, the first, 

 by Dr. J. Agamennone, refers to the earthquake which occurred 

 on December 3, 1887, in the Cosenza Valley. Besides the topo- 

 graphical, a geological map is given, with a description from which 

 we learn that this strip of mountainous land lying between the 

 Gulfs of Tar.'.nto and of Policastro is composed principally of 

 granite and allied rocks with gneisses and schists. The depression t 

 constituting the valley is filled by clays, sand, marls, and other j 

 more or less incoherent rocks of Tertiary age, which have been I 

 eroded by innumerable side valleys into pinnacles, and tongues of \ 

 land with more or less perpendicular sides very liable to slips. 

 Bisignano, which suffered most severely, is situated on some of 

 these pinnacles or almost isolated tongues of molasse. Although 

 the town has been destroyed by nine or ten earthquakes, many 

 of these had iheir foci at soine considerable distance. This last 

 earthquake occurred during a barometric maximum corresponding 

 to a marked centre of high pressure that crossed Europe from 

 December 1-3. and three days after full moon. The author 

 could find no relationship between increase or decrease of micro- 

 seismic movements in Italy and this earthquake. As there were 

 jDrobably three shocks, the first being compaiatively feeble, the 

 people had a'ready escaped from their houses when the second 

 arrived, so that, comparatively to the ruin, few lives were lost. 

 These are the results of the statistics : houses down or threatened 

 ruin, over 900 ; deaths, 22 ; wounded, 60 ; and damage done to 

 the value of i,ooo,coo lire. 



It appe.irs that here stone must be brought from some distance, j 

 and building materials are very dear, hence bad construction and 

 ruin. This but loo well recalls the appalling scenes that passed 

 under the eyes of the writer of this article after the earthquakes 

 of Ischja ' which might have been far less destructive, had it not 

 been for the horribly bad walls, &c. 



From the exceedingly incorrect time kept and the few approxi- 

 mately accurate records, the calculations afford for the velocity 

 of propagation from 650 to 3300 metres per second. 



The author shows that the epicentre was near the station of 

 Mount Gras.nno, and that the greatest damage was on the loose 

 unsupported friable rocks resting inclined against the sloping 

 faces of the older compact rocks — conditions of efHect identical 

 with what occurred in the great Calabrian earthquake of 1783, 

 and noticed by Mallet in 1857. The intensity of this earthquake 

 the author calculates, on somewhat flimsy grounds, at eleven 

 times less than the Andalusian, and four times less than that 

 studied by Mallet in Italy in 1857. The sound seems to have 

 been communicated to much greater distances through the com- 

 pacter and more elastic rocks than through the loose detritic 

 deposits. Wha% however, is strange, is the manner in which the 



' H. J. J. -I.., "Monograph of the Earthquakes of Ischia : a Memoir 

 dealing wiih the Seismic Disturbances in that Island from Remote-it Times, 

 with Special Observations on those of 1881 and 1883." (Naples : Jurcheim, 



rtulhor talks of one shock being subsultory apd another, in the 

 same locality, as undulatoiy, as if they were two entirply different 



kinds of earthquakes. 



' In fine, we pass to the consideration of the Ligurian earth- 

 quake of February 23, 1887 (described by Prof. 'J aramelli and 

 Mgrc^lli), which drove so many people away from the towns of 

 the "Riviera; 'The first eight pages are devoted to the geology of 

 the district, which maybe said to be composed of a range of 

 compact fairly ela<.tic rocks close to the shore-line. The valleys 

 that incise the cliff along the coast extend not only' to the sea 

 line, 'but some distafice beneath the water, whilst near the coast 

 they are partly filled by platforms of late Tertiary, attd very in- 

 coherent deposits. ' It is on these small somewhat triangular 

 planes that most of the towns are met with. The region is one 

 of the most disturbed by earthquakes of Upper Italy, no less than 

 twelve, more or less destructive, occurring since the thirteenth 

 century. 



The authors sent out lico circulars to different localities, and 

 from the' answers were able to obtain much information. It 

 appears that, as' on former occasions, slight shocks were felt over 

 the whole district, and preceded the great one, no less than four 

 occurring during the previous night to February 23, 1887. I'he 

 area affected extended southwards to Rome, Mount Ferrii 

 (Sardinia), east to Pordenone, west to Perpignan, and north to 

 Lyons and Basle. The mesoseismic area was crescentic in shape, 

 100 miles long between Mentone and Albissola. The form was 

 due fo the focus being beneath the sea, and to the region occu- 

 pied by the elastic crystalline rocks. The effects of geological 

 structure in affecting the limitation of isoseismal areas was 

 beautifully illustrated in the Ischian earthquakes described by 

 the reviewer. It is not customary to call the region above men- 

 tioned the mesoseismal area, which should be limited to that 

 space around the epicentre and above the focal area : a better 

 definition would be that of almost total destruction. The zone 

 of severe injury extended to the Langhe of Piedmont and Astig- 

 nano. The limits of severe shaking reach Turin and the lower 

 Canovese, whilst the earthquake was strongly felt as far as 

 Como, Arona, Parma, Leghorn, Marseilles, and nearly all of 

 Corsica. 



The main shock seems to have had two maxima, and to have 

 lasted about 30 seconds. The authors calculated the velocity of 

 projection ^i ()'^m.7i\. OnigVia., 3-53 m. at Faggia, and 47 m. 

 per second at Nice. As in other cases of localities not epicentral, 

 the rumble preceded the shock, the more, the farther the observer 

 was from the focus. 



Azimuths point to the epicentre being 15 miles from the beach, 

 midway between Oniglia and San Remo, which is confirmed by 

 the isoseismals being concentric to a point 20 kilometres south 

 of Porto Maurizio. The shock appears to have started at about 

 6.19 a.m. The velocity of propagation was calculated at 1452 

 m. per second westward, and 584 m. per second towards Genoa : 

 this the authors consider to be due to a main and secondary focus, 

 whilst the depth obtained from emergence angles appears to be 18 

 kilometres. Little disturbance of the sea occurred, but it is said 

 to have remained at a lower level for some days at Loano and 

 Porto Maurizio. Dead fish of deep-sea character were found along 

 the coast some days after. No meteorological phenomena of 

 importance were noted, but strong telluric currents were set up 

 at the moment of the earthquake. After nine minutes, another de- 

 structive shock occurred, another at 8.53 (M.T. Rome), and in 

 the ruined area there occurred another twenty-two slight shocks, 

 and others continued to occur with dimini-hed force to March 

 II, so that at Savona fifty were perceptible in all. 



The first three earthquakes kilkd 640 persons, and wounded 

 as many, and the damage in the provinces of Porto Maurizio, 

 Albenga, and Sivona, was valued at 21,500,000 lire. 



The greatest damage occurred on thin layers of incoherent 

 rocks superposed on the more elastic and crystalline ones, at 

 sharp boundary lines of different rocks, and unfavourable topo- 

 graphical positions. The effects were augmented by bad and 

 unscientific construction of the houses, or badly repaired 

 buildings, that have suffered in former shocks. 



In this article, already of inordinate length, fair justice has 

 hardly been done to the works reviewed, but the reader will see 

 that Italy is awaking to her duty towards humanity and science 

 in organizing the study of her seismic phenomena, and shaking 

 off that conservatism and isolation which ruled her in this 

 department up to the year after the great Ischian earthquake. 



H. J. Johnston- La VIS. 



