Geological Results of the Earth’s Contraction. 181 
place as a consequence of contraction below a stiffened crust ; 
we know them to be a necessary effect. We see also that de- 
pressions would somewhere follow a fracture, and the lateral pres- 
sure exerted would be likely to dislocate, often raising and neces- 
sarily propping or supporting as it raised. We understand that 
such fissurings, whether internal or external, would cause shak- 
ings of the earth (earthquakes) of great violence, and in all peri- 
ods of the earth’s history, and it might be over a hemisphere at 
vast areas like the oceans would draw off the waters from the 
land; and by the several combined effects of the cause under 
consideration, oscillations in the water level would take place. 
These effects have been briefly stated in the preceding number 
of this Journal.* ' The theory appears to us to be more worthy 
* See page 95.—The principles may perhaps be rendered more clear by means 
of the following figures. In fig. 1, the crust (ct) is represented covered with wa- 
r 3 
- ter (00'). In fig. 2, the globe has contracted from the dotted line to ¢’t! ; c’o, olt', 
oo portions free from volcanic action, ( almost entirely with 
as was the ¢ 
parts corresponding to the continents in the Silurian périod ;) p is an area of wa- 
Fig. 2. 
r 
ni r 
ter upon o!t!. oo! represents the incipient oceanic depression, over which, owing 
to its igneous character and thinner crust, (this Journal, ii, 352,) contraction went 
On the most rapidly, and where, atthe same time, Igneous ejections and displace- 
fall in the water level. 
= bsi m 
place from increasing tension preaing a paroxysmal relief by fractures, and 
Fig. 3. 
As the crust below the oceanic depression becomes thicker by cooling, the con- 
traction, not now causing fractures and upliftings over Its own area alone, would 
uce a tension laterally against the non-contracting area and occasion pressure, 
res, and u vals; veg thus the elevations m, 7, T, S, fig. 3, ‘ 
From this figure, the fact will be appreciated that the amount of effect, claimed for 
