48 REPORT—1850. 
surveying voyages of the Leven and Barracouta, on the east coast of Africa, 
in 1821 and following years, vol. i. p. 288. One of the ships was nearly 
wrecked off Quilimani by one of these rollers, “which burst with fury on 
the decks, bearing everything before it, nearly swamping the ship, and 
throwing her on her beam ends.” 5 
Capt. Owen says, “ The roller moves as a precipitous hill of water from 
10 to 50 feet in height, overwhelming everything in its course. They are 
observed on all the shores of the Atlantic south of 30° N. lat., sometimes 
rising in a perfect calm, probably from past gales in distant parts; but their 
true cause is not yet known.’”—Owen, Voyages, p. 288. 
We now pass to some remarks upon the secondary effects produced by the 
proper phznomena of earthquakes, viz. by those which we have already 
treated of. 
Again let it be observed, that most authors have very confused notions as to 
the essentially different nature of earthquakes and of permanent elevations or 
depressions of land. An earthquake, however great, is incapable of producing 
any permanent elevation or depression of land whatever ; its functions of eles 
vation and depression are limited solely to the sudden rise and as immediate 
fall, of that limited portion of the surface through which the great wave is 
actually passing, momentarily. Hence, it is inexact, or rather untrue, to class 
earthquakes as amongst the causes of permanent elevation or depression of 
the land. But as earthquakes are unquestionably closely connected with vol- 
canice forces, and with those nearly identical forces upon which permanent 
elevations and depressions without eruption depend, so there are few earths 
quakes of any magnitude that are not accompanied by permanent eleva 
tions and depressions of the land. These and the earthquake have a common 
origin, and are to be regarded as each the symptom of the other; but while 
the elevation or depression of the land may cause the earthquake, or rather 
be the immediately forerunning event to the earthquake, the earthquake can 
never cause the permanent elevation or depression of the land. I dwell upon 
this because it is important to our future progress in earthquake knowledge, 
that we should form a clear conception of what it is, and how far its limits 
extend, and clearly distinguish these from both the permanent elevations and 
depressions, often of vast extent, that accompany their occurrence due to the 
great elevatory forces of the interior of our planet, and also from all those 
secondary, or doubly secondary phenomena, which change the face of the 
country shaken, but which are only contingent and accidental effects of the 
earthquake, and which vary with the local conditions of the country in which 
they occur. The confusion resulting from having lost sight wholly of this 
distinction is well seen in the extracts [ have given from Hooke’s discourses 
of earthquakes in a preceding part of this Report. | 
In reading over the narratives of earthquakes at large, we are constantly told 
of mountains being removed from one place to another, of valleys being oblite- 
rated, of the course of rivers being altered, springs and fountains spouting up, 
fissures and chasms of vast depth and extent being formed, with smoke and 
flames issuing from them, lakes formed where none were before, and so forth; 
all of which are said in a word to have been produced by the earthquake. 
For example :—* Terres quoque motus profundunt sorbentque aquas; 
sicut cirea Pheneum Arcadia quinquies accidisse constat. Sic et in Coryco 
monte amnis erupit posteaque cceptus est coli. Illa mutatio mira ubi causa 
nulla evidens apparet; sicut in Magnesia calidas factas frigidas: salis nom 
mutatursapore. Et in Caria, ubi Neptuni templum est, amnis qui fuerat ante 
dulcis mutatus in salem est..... : ) 
“ Rhodiorum fons in Chersoneso nono anno purgamenta egerit. Mutantur 
