Mr. Matter on the Dynamics of Earthquakes. 101 
possibly known, and to revel in the old and, under various shapes, ever-recurring 
myths of geognosy.””* 
It is to be wished that something more of this spirit were transferred to the 
fact-worshipping geologists of our day. 
Geology, like every other department of inductive science, to be successfully 
pursued, must at times be followed by the high a prior? road; an elevation must be 
attained which, without superseding the collection and the colligation of facts, 
shall enable us to look down upon and explain them, by seeing their order, con- 
nexion, and agreement with the laws of mechanics, physics, and chemistry. 
DESCRIPTION OF THE PLATES. 
Pruate I.—Map or EartuquakE coTipaL Lines. 
This represents an imaginary portion of the earth’s surface, the seat of earthquake 
disturbance ; the forms of the coast, the depth of soundings, and the geological formations 
of the land, have been arranged for the purpose of evidencing, through the eye, the rela- 
tions, to them and to each other, of the elastic earth wave or shock, and of the great sea wave. 
The uncoloured portions of the map represent the sea, the depth of soundings of which 
are given in two sections, intersecting at right angles, through the point which is the 
origin of the earthquake impulse. These sections, coloured dark grey, shew, by the 
method commonly called “ sectio-planography,” the depths along the right lines forming 
their upper boundaries, which are on the surface of the water. 
The land and the bottom of the intervening sea are supposed to consist of four distinct 
formations, or rather classes of formations, differing in depth and in elasticity, viz. : 
1. Post-tertiary and tertiary deposits. Coloured Yellow. 
2. Upper sedimentary, non-crystallized rock. Coloured Gray. 
3. Lower sedimentary rocks, either stratified, laminated, or erystallized. Coloured Blue. 
4. Igneous or metamorphic, crystallized rocks. Coloured Red. 
Each of these classes may combine several groups of formation, but it is supposed that 
the properties, as a whole, of each class, as to elasticity, &c., are in the above order, pro- 
ceeding from the least to the most elastic. 
* Page 252. 
