292 W, O. CROSBY 
deposits, although in part widespread, are, nevertheless, charac- 
teristic of but a small fraction of the land surface, and are likely, 
except, in general, under graben conditions (localized depressions), 
to be relatively thin. They are also, in large part, transitory, 
being ultimately (perhaps during subsidence) reworked and 
deposited in the coastal province. Also, the oceanic or truly 
abyssal deposits, although of relatively limitless area, are espe- 
cially noteworthy for their thinness and their wonderful uniformity 
over wide expanses. 
The coastal zone or province, although the narrowest, is, then, 
as every student knows, the specially important field of relatively 
permanent sedimentation. In other words, the old, broad generali- 
zation still holds, that sediments are derived from the land and 
deposited in the sea, and chiefly in the marginal portion of the sea; 
although the finer part of the terrigenous (non-cosmic) detritus may 
reach the abyssal or truly oceanic depths. The calcareous and 
siliceous oozes characteristic of the deep sea are, it may be observed 
in passing, truly land-derived, although the material is transported 
in solution and deposited by organic agency. 
Again, in the terrestrial province the sediments are during 
their deposition almost constantly exposed to erosion. Contem- 
poraneous erosion and deposition is peculiarly characteristic of 
this province, and the frequent occurrence of the resultant pseudo- 
unconformity tends to make the recognition of true or significant 
unconformity difficult. In the oceanic province, on the other hand, 
uniformity and conformity reign supreme and unconformity is 
virtually wanting. But in the coastal province the migrations of 
the shore are extremely favorable to the alternation of deposition 
and erosion over extensive areas and the development of true or 
normal unconformity. 
The grand result of sedimentary activity in the coastal prov- 
ince is the building of the broad bench or terrace fringing the con- 
tinent, of which the dry, landward portion is known as the coastal 
plain and the wet, seaward -portion as the continental platform; 
and nowhere, probably, has the coastal province a more normal 
development than on the Atlantic and Gulf borders of North 
America. 
