22 REPORT—1850. 
tion du nord au sud, il fallait replier la cause vers sa veritable direction qui 
était du sud au nord.” 
He divides earthquake movements into three classes—“en verticaux ou 
directs, en horizontauz ou indirects, et en circulaires ou accidentels, comme ni 
tenant 4 aucune cause, ni a aucun systéme regulier.” 
After explaining that by the first he means direct upward and downward 
motion over the volcanic centre, “et proviennent du gouflement de la matiére,” 
he proceeds to the horizontal motions :— 
“Ce mouvement ondulatoire ressemble aux vagues de la mer, et ne dure, 
comme tous les tremblemens de terre, que peu d'instans; du moment ou 
lélévation s'est fait, elle s’abaisse de suite, et ne reste jamais permanente. 
Un tremblement de terre quelque violent qu'il soit ne peut éléver le terrain 
que par ondulation de 4 a 5 pieds au plus.” 
He here, and in the succeeding passage, clearly recognizes the difference so 
usually overlooked, between the transient elevation, and as immediate de- 
pression of surface due to the passage of the earthquake shock, and the per- 
manent elevation produced directly by volcanic action from beneath. 
He seems to have had small knowledge of the facts of great sea-waves ; 
and seems (p. 378) to consider them sufficiently explained by “the contra- 
dictory effects” in producing a surge, of severe shocks taking place under 
the sea bottom. 
Although horizontal shocks are indirect and only “la conséquence d’une 
cause directe ou de son contrecoup,” he considers they produce more 
formidable effects than the direct or vertical ones; but he does not get at 
the true cause: he says, “ cela dépend des corps conducteurs et de la forma- 
tion du sol, car il existe dans l’intérieur de la terre d’immenses cavernes sur 
lesquelles la croute superficielle n'est pour ainsi dire que suspendue;” and a 
violent direct shock, he thinks may throw these fragile crusts down at a 
distance, and bury cities, &c. 
And as to the third class, or “ secousses accidentelles,” he is of opinion 
that they are due only to the occasional and capricious falling in of such 
cavities, and are in fact not properly a part of earthquake phenomena at all 
—an easy way of disposing of the question. 
One of the most remarkable of the author’s conclusions is, that,—“ La 
distance ἃ laquelle les tremblemens de terre étendent leur choes, dépend 
en premier lieu de la profondeur du foyer dans lequel la commotion s'est 
développée, en second lieu de la liaison des conducteurs du mouvement dans 
lintérieur de la terre.” 
It is to be borne in mind that his “conducteurs” are not solid vibratory 
bodies, but always hollow tubes or ducts in the interior of the cavernous 
earth. 
In page 385, in a passage too long for transcript, Bylandt well insists upon 
the impossibility of earthquakes being properly considered as causes or 
means of geologic elevation, but simply effects and symptoms of the action 
elsewhere of the great elevatory forces acting slowly from beneath. 
He proceeds :—“ Mais aprés avoir comparé les tremblemens de terre entre 
eux, définissons les mathématiquement, et éprouvons que les effets des tremble. 
mens de terre, sont entre eux en raison inverse du carré de distance de chaque 
point de la surface au centre du foyer.” Those who desire to know the 
author’s demonstration of this, and that the effects of earthquake shocks are in 
the opposite direction to the shocks themselves (owing to the inertia of 
the bodies overthrown), must refer to the work itself, and to the very curious 
atlas of plates and diagrams accompanying it. One of Bylandt’s diagrams, 
