32 The American Geologist. July, 1893 
//. Formation of Sediments, 
(a) General Statement. 
Products of rock disintegration and decay may aid in rock for- 
mation in either of six ways: 1st, they may remain in place and, 
unmoved, be buried beneath sediments, — such may be the 
fate of any of the residual soils at present exsting; 2d, they 
may be transported a short distance by ' 'surface wash" or ' 'creep, " 
as in arid regions; or, 3d, they ma}' be removed by wind; or, 4th, 
by ice; or, 5th, by rivers; or, 6th, by the sea. These will be 
taken up for consideration in their order. The first needs no es- 
pecial mention, other than that already given it. One case where 
the products of disintegration have been buried in place, chiefly 
under their own overlying, decayed material, removed but a short 
distance, will be described in the latter part of the essa}', under 
the discussion of sediments derived by the action of the sea di- 
rect. 
{!>) By Surface Wash. 
Peculiar conditions exist in arid regions. Thorough rock de- 
cay is rarely if ever found in such places, for the reason that the 
essential elements of water and vegetable acids are not present in 
any considerable quantities. A certain amount of disintegration 
takes place, but there is little vegetation to hold the soil in place, 
and its almost constant dryness makes it an eas}' prey to the 
wind, by which the finer particles are blown hither and thither. 
The peculiarity of rainfall brings about another condition — the 
phenomenon of surface wash or creep. The rare rains which fall, 
generally come in copious downfalls, and, as they fall on a sur- 
face which is parched and dry, they are often very quickly ab- 
sorbed by the soil. Such desert regions are, as a rule, not occu- 
pied by well established drainage ways. The rains which are 
sufficiently copious to run off are rare, and the channels which 
they carve are often partially obliterated before another such rain 
occurs. There are broad tracts on vv^hich the rain finds no well 
established water-ways b}' which to escape. As it soaks into the 
parched, barren, and generally sandy soil, it tends to flow down 
the grade, and, in so doing, to carry some of the soil along with 
it ; but often before the force of the accumulating waters is suffi- 
cient to carve distinct channels, the rains have ceased. Floods 
from violent cloudbursts in such places frequently become a mov- 
ing mass of mud at their lower course. 
