234 REPORT — 1861. 



creased degree of discontinuity and shattering, in the directions approaching 

 that of lamination, or transverse to the wave-path in the first case. 



It is necessary to guard against any misconception as to the import of this 

 result. The fact ascertained and just enunciated is this, that the velocity of 

 wave-transmission is greater in the material of these rocks in a direction 

 across their lamination than in one longitudinal to the same, provided or 

 assuming the material he perfectly unshuttered in both — as homogeneous, in 

 fact, as the small specimen-cubes experimented upon. And were the whole 

 mass of the rock, as it lies in the mountain-bed, as homogeneous as such 

 cubes, then the velocity of wave-transmission would actually be greater 

 across long ranges of natural lamination, than edgeways to them. The oppo- 

 site, however, is often the case ; the wave-transit period is slower as the 

 range of rocky mass is more shattered, discontinuous and dislocated. 



These conditions most affect rocks in nature in or about their planes of 

 bedding, lamination, &c., and hence most retard wave-impulses transverse 

 to these planes ; so that the more rapid ivave-transmissive power of the 

 material of the rock in a directum transverse to the lamination may be more 

 than counterbalanced by the discontinuity of its mass transverse to the same 

 direction. 



The results of Wertheim, on the transmission of sound in timber, 

 proved the velocity to be greatest in a direction longitudinal to the fibres 

 and annual layers of wood ; less in a direction perpendicular to the same, 

 and radially outwards from the centre of the tree towards its exterior; and 

 least of all in a direction, qicam prox., parallel to the annual rings, and per- 

 pendicular to the longitudinal fibres ; that is to say, in eac!) case the velocity 

 of sound was rapid in proportion to the less compressibility of the wood in 

 the same direction. His results might seem at first to conflict with those 

 which I have announced. Any such conclusion, however, would be a mistake; 

 on the contrary, my results perfectly analogize with those above alluded to. 

 The difference between the cases is, that wood in mass, however large, is 

 practically homogeneous and unshattered, and that its direction of least 

 compressibility is longitudinal to its lamin(B (or annual layers) ; whereas the 

 direction of least compressibility of rock is transverse to its lamince which 

 have been already powerfully compressed in this direction. In fact, as 

 respects the question here in point, there is no true analogy in structure 

 between the lamination (by annual rings) of wood, and the lamination or 

 bedding of rock. 



It follows from what precedes, that earthquakes and rocks, as both ac- 

 tually occur in nature, — the rocks being of a stratified or laminated form 

 (generally all sedimentary rocks), — must present the following conditions as 

 to rate of transit of shock : — 



1st. If such rocks were perfectly unshattered, and the beds or laminae in 

 absolute contact, the shock would be transmitted more rapidly across these 

 than in their own direction. 



The difference is more in favour of the transverse line, in proportion as 

 the rock is made up more of angular sedimentary particles of very unequal 

 dimensions, the longest being parallel to the general lamination, and in 

 proportion as the imbedding paste is softer in relation to such particles. 



Some sedimentary rocks no doubt exist, made up of particles perfectly 

 uniform and equal in all three dimensions, and without imbedding paste — 

 such as the lithographic stones of Germany, the Apeunine marl-beds, &c., 

 in which (assuming the above condition as to continuity) the transit-period 

 would be alike in all directions probably. 



2nd. The actual amount of shattering and discontinuity in nature being 



