(hi ('i/rli's of Sidniniifiltnni. \\ tJI iii inx. •^)17 
;is the sixth power of the veloeity. (Hopkins (^. J. (ieol. 8oc. 
Vlll p. 27.) These hist will have a size relative to the first as 
small colible-stoiies to <iravel. Now let us suppose the i)rocess of 
erosion continues. The coai'se fragments will be polished and 
rounded l»y their journey to the sea. and will be deposited in a 
soft matrix of mud and tiner i)et)V)les as a eonjilomerate. The 
largest fragments will l»e deposited first, and. with the wearing 
away of the slope, and consequent diminution of the angle 
of slope, the size of the pebbles of successive deposits 
will be smaller and smaller. Finally, when the angle of slope be- 
comes such that the velocity is one-half what it was at first, the 
jsize of the fragments will be 1 instead of (!4. Such fragments 
Avill become a sandstone or shale according to circumstances. At 
length the land will ]>e entirely eroded away. Meantime the sed- 
iments deposited along its shores will have accumulated to a vast 
depth. This accumulated weight will necessitate a sul)mergence 
to restxnv the eciuilibrinni of surface jiressuri's (^Bal)bage and Prof. 
-Jas. Hall). The deposits will sink to a depth which will l)e con- 
genial to the development of vast populations of corals, crinoids 
and other lime-secreting organisms. Here they may continue to 
build through a long succession of geiu'rations, the increment of 
Aveight due to their accumulation producing just enough submer- 
gence to maintain a projH'r level for their growth (Darwin). A 
vast deposit of crude limestone will be tiie I'esult. This is pre- 
<Msely the succession found in the table at the beginning of this 
article. (V>nglomerate. sandstone and limestone are repeated 
over and over again. in the pi'eceding discussion we have 
assumed the simplest conditions imaginable; aueminenceof land, 
a given elevation subject to no oscillations of level during the 
long period of time while it is worn down to the level of the sea. 
an e(}uable :ind unifoiin ((uantity of precipitation, and a suffi- 
cient weight in the accumulated sediments to effect a subsidence 
wiuMi the destruction of the land was (completed, and. liually. a 
subsidence deep enough and not too deep to tie f;ivorable to the 
growth of lime-secreting organisms. 
it is astonishing to see how faithfully these ideal condi- 
tions have l»een repeate(lly realized as recorded in the l*al- 
;eozoic I'ocks of North .\nu*ric:i. .Vnd it is perfectly cou- 
eeivabh' how a variation of these ideal conditions might lead 
to the discrepancies and anomalies already alluded t<>. ^^'e 
