42. REPORT—1858. 
illustrious physicist whom I have just quoted includes the Azores and 
Canaries in the seismic region of the Mediterranean. 
They would seem to form the western part of an axis which extends to 
Hindostan with variable shades, and thus unites the Atlantic with the great 
volcanic chain of the Sonde (Sunda), which, as we know, is connected by 
the Japanese and Kurile Islands with the Aleutian Archipelago, and by this 
chain to the grand volcanic range of the two Americas. This idea is in- 
genious, but is ittrue? It is a point that I cannot at present discuss. Yet 
we must admit that the Azores, and even the Canaries, seem to form a part 
of the sphere of subterranean convulsions, the centre of which is almost 
parallel to Lisbon ; and to be at the western extremity of that great seismic 
zone which proceeds by the peninsulas of Spain, Italy, and Greece, to the 
volcanoes of Asia Minor, and which there joins the central chain of Asia. 
It is, in fact, within this zone, extending towards the north as far as the Car- 
pathian Mountains, that the principal centres of earthquakes and the most 
remarkable seismic axes in Europe are to be found. Extending to the 
west along the 40th parallel, this zone reaches the United States of Ame- 
rica, where it embraces New York and Boston, which M. Berghaus has per- 
haps marked with a rather too dark colour, though earthquakes are not rare 
there ; and thence it proceeds to Kentucky, Tennessee, and Missouri, where 
the phenomena of the year 1811 demand a darker shade in M. Berghaus’s 
beautiful map. M. Berghaus draws a linear region in Arabia, from Medina 
to Yemen, along the east coast of the Red Sea. Can this be a partial 
axis of convulsion? Is it independent of the Mediterranean zone? Or is 
it united to it by a second axis—the Syrian axis, parallel to the east coast 
of the Mediterranean? But the countries near to the Isthmus of Suez ap- 
pear little subject to earthquakes ; can there be a solution of continuity 
between these two axes ? or does the space which divides them, and where the 
phenomenon has, so far, been so rarely remarked, constantly present a pecu- 
liarity verified more than once in America? In the New World (at Ca- 
raccas, for example) certain regions of small extent have been observed to 
enjoy a complete calm while the neighbouring country experienced fright- 
ful catastrophes. 
The historians of these disasters have characterized this unconvulsed part 
of the soil by a picturesque expression, namely, “a bridge has been formed.” 
The probable physical explanation of this phenomenon of “the bridge” has 
been given in a former Report (2nd Report, p. 309), by the author of this, 
based upon the view that total reflection of elastic impulses may occur under 
certain suitable conditions. 
Perrey continues, “ No simultaneous convulsions at both extremities of 
this Syro-Arabic linear region have been recorded. However, if we recall 
that the Himalaya Mountains are very subject to subterranean convulsions ; 
that the Alps, and especially the Pyrenees, are frequently shaken, the Cau- 
casus-range still oftener, and that the Andes are almost always in a state of 
commotion ; must we not regret that we possess no information concerning 
the phenomena in the high Ethiopian chain? is it not to be desired that 
travellers in Africa should make observations upon a matter so interesting 
to science? 
“ During the last few years Abyssinia (strongly marked in M. Berghaus’s 
map) has been the study of numerous French explorers. Several narratives 
of their vast and useful labours have appeared ; but I do not find one word 
about earthquakes! The Academy of Sciences has just given new instrue- 
tions to’ M. Rochet (d’Héricourt), about to undertake a third expedition to 
that country ; and the phenomenon is not even mentioned by M. Duperrey! 
