Relation of Secular Decay of Bochs.- — Ta'n\ 43 
rived. Plainly, a rapid encroachment of the sea on the land is 
necessary to admit of such a partial working over. The ordinary 
movements of the land are so slow that all such loose material 
would be removed. Cases where the secularly decayed soil is 
found buried in place, or only slightly removed from its place of 
origin must, therefore, be relatively rare. The evidence of the ex- 
istence of this kind of material during the periods of the past 
must, for the most part, be looked for in sediments removed some 
distance from their source. The mechanical and chemical con- 
stitution of such sediments ought to serve as a key to indicate 
their origin. 
{g) Summary. 
From what has been written it will lie seen that secular disinte- 
gration may be an important source for the origin of sediments 
which may be derived from it in various ways. It may be trans- 
ported to its resting place in the process of I'ock building, by the 
wind, by ice, by running water or b}' the sea. A country chang- 
ing in climate from moist to dry is subject to atrial action of 
considerable uniformit}^ and intensity, and an accumulated resid- 
ual soil may thus be swept away ; the change from temperate to cold, 
the coming on of an ice period, brings about other conditions liy 
which accumulated soils are removed. China seems to offer an 
instance of the former, New England of the latter. 
Changes in land elevation ma}' admit of the accumulation of 
a residual soil or the removal of one already accumulated. A 
country long standing at a certain elevation is favorably situated 
for soil accumulation. The elevation of such a land gives to the 
streams new powers, and l)y this means the residual soils and dis- 
integrated materials ma}' be removed. The same countr}' de- 
pressed brings the soil within reach of the waves. 
Accompanying these changes there must be much destruction of 
life. The clear-water dwelling fauna of the shore, driven out by 
the appearance of mud-laden waters, is replaced by aditl'erent fauna. 
So there may have been alternations of faunas from this reason, as 
well as alternations of sedimentation, first rapid, then slow depo- 
sition. 
The importance of secular disintegration along tiie lines above 
suggested is not fully understood and seems to have been gener- 
ally overlooked by geologists. Secularly decayed soils exist at 
present and they must have existed in the past; lands have been 
