58 
DUTTON. 
there is nothing to indicate any cause of deflection. They 
are found on the tundras of Siberia and the monotonous ex¬ 
panse of British North America, where the surface of the 
earth is but feebly diversified. In mountain regions they 
are often conflicting and unintelligible, but along the sea 
coast the indications are more systematic. On both the At¬ 
lantic and Pacific shores the deflection of the plummet is 
almost invariably towards the ocean, and is often of consid¬ 
erable amount; but it is along the shore that the- isostatic 
theory would lead us to look for just this deflection, for it 
is along the margins of the continents that great bodies of 
sediment accumulate; and so long as the earth possesses any 
noteworthy degree of rigidity, enabling it to sustain in part 
the resulting deformation of isostasy, so long must we expect 
to find these sediments constituting an excess of mass whose 
attraction will make itself felt upon the plummet. 
The theory of isostasy thus briefly sketched out is essen¬ 
tially the theory of Babbage and Herschel, propounded nearly 
a century ago. It is, however, presented in a modified form, 
in a new dress, and in greater detail. We may now proceed 
to deduce some important consequences. 
A little reflection must satisfy us that the secular erosion 
of the land and the deposit of sediment along the shore lines 
constitute a continuous disturbance of isostasy. The land 
is ever impoverished of material—is continuously unloaded; 
the littoral is as continuously loaded up. The resultant forces 
of gravitation tend to elevate the eroded land and to depress 
the littoral to their respective isostatic levels. Whether these 
forces shall become kinetic and produce actual movement or 
flow will depend, first, upon their intensity; second, upon the 
rigidity of the earth by which such movement is resisted. 
Let us consider, then, the intensity of the forces. 
The littoral belts upon which sediments are thrown down 
are coextensive in length with shores. Their widths are no 
doubt variable, but must often reach a hundred miles or 
more with considerable thickness, and are not wholly unim¬ 
portant at much greater distances. The thickness of the de- 
