22 



♦ KNOWLEDGE ♦ 



[Nov. 11, 1881. 



first H'limdor you sec rpstinf; on the sandy bed of the 

 Aiiuariiim-tank, and you will recpive ample proof of the 

 truth of the foregoing remarks. And should you chance to 

 see the lazy " monk," or angel-Cish, as it lies prone, heavy, 

 and indolent in the highest degree in the flow of its tank, 

 you may again understimd something of the value of colour 

 as a means of protection to animal life. 



In the case of those " queer fislies," the little sea-horses, 

 or hippocampi, with heads like horses, and with a body 

 which, at large, reminds one most forcibly of some figure 

 from the Heralds' College on a crest, concealment is 

 effected in a slightly different fashion from that prevalent 

 among the soles. Here the body, as a rule, possesses long 

 streamers or fringes tliat mimic the seaweeds ; so that, as 

 the animal reposes, its body may well enough represent a 

 stone, to which are attaclied fragments of marine vegeta- 

 tion. The Australian sea-horses, which live among red 

 seaweeds, have streamers of that hue attached to their 

 bodies, and the mimicry and imitation of their surroundings 

 are thus very complete. Even their near neighbours, the 

 pipe-fishes, with green l)odies, when they fasten themselves 

 to some fixed object, and " loll " in the water, may closely 

 resemble an inert piece of green weed. 



Amongst even the highest animals, protective colouring 

 is common. A lion's hue matches the sand, as a tiger's 

 stripes, according to Mr. Wallace, imitate very closely the 

 foliage and trees amidst which it crouches. The camel's 

 coat is sandy like its desert ; and the rabbits offer as plain 

 examples as any of the colour harmony in question. The 

 polar bear is white, like the arctic fox in winter dress ; 

 and the nocturnal rats and moles are dressed in shades 

 the opposite of the ghost-like hues that become so con- 

 spicuous at night. 



THE SOUTH EUROPEAN VOLCANIC 

 SYSTEM. 



rnHERE are reasons for believing that all the volcanoes — 

 X and, indeed, all the regions of subterranean dis- 

 turbance in Southern Europe — belong to a single volcanic 

 system. 



It is, indeed, rather difficult to define the exact relation 

 between the different parts of a widely-extended volcanic 

 region. At a first view it seems unreasonable to assert 

 that if eruptions or other forms of disturbance in different 

 places are simultaneous, this must be regarded as evidence 

 that the two places belong to the same volcanian region, 

 while a similar conclusion should be deduced from the fact 

 that quiescence in one spot synchronises with disturbance 

 in another, and vice versa. For instance, it was noticed 

 that during the often-interrupted eruption of Vesuvius in 

 1868, Etna was more or less disturbed, until at length, as 

 if in sympathy with the Keapolitan volcano, the Sicilian 

 mountain gave vent to enormous streams of molten matter ; 

 and this of itself might be considered to afford satisfac 

 tory evidence of the existence of some sort of connection 

 between Etna and Vesiunus. But on the other hand, 

 we are told that when the great earthquake of Calabria 

 took place early in 1783, the inhabitants of Pizzo 

 remarked that the volcano of Stromboli, which is in 

 full view of Pizzo at a distance of about fifty miles, 

 smoked less and threw up a less quantity of he.ited 

 matter than it had done for several preceding years. 

 Then, a^ain, on the same occasion the great crater of Etna 

 gave out enormous quantities of vapour as the Calabrian 

 earthquake began, while Stromboli seemed exceptionally 

 active as the commotion of the earth in Calabria began to 

 diminish : yet no eruption occurred from cither of those 



great vents during the whole progress of the Calabrian 

 earthquakes. Are we to infer from thLs, as in one place 

 Sir C. Lyell seems to do, that the volcanic tires of Etna 

 and Stromboli are "very independent of each other," or 

 that the same mutual relation exists between them as 

 between Vesuvius and the volcanoes of the Phlegrsean 

 Fields and Ischia, " a violent disturbance in one di.strict 

 serving as a safety-valve to the other?" Lyell complet<-.'i 

 the latter sentence, by the way, by adding, "lx)th never 

 being in full activity at once." But here it seems to us he 

 loses the full value of the evidence which the various dis- 

 turbances of the South European volcanic regions have 

 afforded. Rightly viewed, both forms of evidence equally 

 tend to sliow the inter-dependence, neither showing the inde- 

 pendence, of different parts of this great region. If an 

 eruption of Vesuvius begins precisely w^hen an eruption of 

 Etna seems for some cause or other to be checked, or 

 diminished in actiN'ity, the circumstance seems in itself to 

 suggest, if it does not prove, that the two vents ser\ e to 

 relieve one and the same volcanic region. If, again, 

 Vesuvius and Etna both burst suddenly into violent erup- 

 tion at one and the same time, surely that also is evidence' 

 that they belong to the same volcanian system. 



There is no reason whatever for assuming that because 

 a disturbance in one region may serve as a .safety-valve for 

 another, therefore both can never be in full activity at once. 

 Experience has shown repeatedly that two regions of 

 volcanic disturbance, the movements of which .sometimes 

 alternate, may at other times be simultaneously active. 



But it may perhaps be asked, if this really is so, how can 

 we possibly decide whether any two volcanian regions what^ 

 ever are connected or distinct 1 For instance, when Chim- 

 borazo is active, Vesuvius is either active or at rest. If 

 Vesuvius is active, the two vents may be said to be working 

 simultaneously ; and so the preposterous idea may be 

 adopted that these two volcanoes, though separated by so 

 many thousands of miles, relieve the same region of sub- 

 terranean disturbance. If, on the other hand, when Chim- 

 borazo is active, Vesuvius is at rest, then the same absurcf 

 conclusion is derived fi-om the consideration that the action 

 of Chimborazo alternates with that of Vesuvius. In reality, 

 however, plausible though this objection seems, it has no 

 weight. The distinction lietween the simultaneity or the 

 reverse of the action of Ve-suvius and that of Chimborazo, 

 and the associated or alternated efforts by which Vesuvius 

 and Etna, or Etna and Stroml)oli, or Vesuvius and the 

 Phlegr.-ean Fields, relie\e one and the same region of sub- 

 terranean disturbance, is sufficiently well marked. Com- 

 pare the dates of the eruptions of Chimborazo and 

 Vesuvius with the actual range of time over which the 

 observations extend, and no connection whatever can be 

 observed between them. Vesuvius must, indeed, be either 

 quiescent or at rest when Chimborazo is in eruption, but 

 Vesuvius never (or only by the merest accident) begins to 

 be disturbed when an eruption of Chimborazo commences ; 

 nor has an eruption of Chimborazo ever synchronised, 

 except by the merest accident, with the cessation of an 

 eruptinn of Vesuvius, or vice vrfd. But whether we find 

 that an eruption of Vesuvius ceases very soon after an 

 eruption of Etna has begun, or that both volcanoes burst 

 at once, or nearly at once, into eruption, the coincidence of 

 contrasted conditions implies equally with the coincidence 

 of similar conditions, that the two volcanoes are outlets of 

 the same volcanic region. 



In other large regions of suViterranean activity we notice 

 similar relations — namely, at times periods of well- 

 marked oscillatory disturbance, and at other times periods 

 of simultaneous action. We also find volcanic regions 

 where the outlets are nearlv alwavs in action together at 



