22 The American (jieologtKt. .Tamuny, i«93. 
ON PLEISTOCENE CHANGES OF LEVEL IN EAST- 
ERN NORTH AMERICA.- 
r>V liAUON (iKIJAItl) 1)K tiKKl;. StOlUhllllll. Swcdt'ii. 
One of the most important principles niK>ii wliicli <i('olo<>y is 
founded is the tlieorv of continental clianges of level. Tlie- 
main points f>f this theory seem, in seve-ral cases, to have l»een 
■well established l)y Amerit-an lieoloiiists. 'i'lius it has heeiv 
pointed out. tliat to account for sandst»>ne several thousand feet 
,in thickness, and other deposits in shallow water, it is necessary 
. to assume that the sea-bottom was sinkin«>: at the same rate that 
the sediment was accunndatini>'. A*>ain, as the continents in 
certain instances for lonu pi'riods of time have not lost in hij^ht^ 
, and this notwithstandini>' their immcuisf denudation, they must 
have been gradually risiiii>. It is also vei-y licneially admittedl 
that many of the al»undant alternations of strata <ieposited ,dur- 
insi' ditferent l»athy metrical conditions, as well as the lu'eaks be- 
, tween them, were caused Uy the oscillations of the eai'th's crust. 
, In many instances, however, it cannot lie d^ecidi'd whethci' the 
change of level was really due to moveni<'n;ts of the land, or 
whether it was only the surface of tin- sea that rose and fell.. 
Since the eminent Austrian <:eolosi"ist. K. Suess. in his grand 
work "Antlitz (U'r Krde has in a very ingenious way tried to re- 
fer most of the oscillations to the latter cause, denying the i-ising 
,of the continents altogether, and since his views have been 
adopted liy many geologists, it si'cnis paiticularly desiral)le to- 
get njore positive facts for the Hnal si-ttlement of the ((Uestion. 
Kor the present at least it is hard to get such facts concei'uing the- 
older formations, as they are xciv often enxUMl away to a greater 
or less extent and concealed l»v younger deposits. It is thus iui 
,m«tst cases impossil»le to ih'termine the original extent of a cer- 
tain layer and especially of tlii' sea in which it was formed. 
Conseipieutly we c.-mnot (h'termine with snllicient at-curacy in 
■ what way the corresponding geoid-snrface has l»een (hd'ormed. 
In regard to the Plif)cene and IMeistocene foimations it is of 
.course less dillicult. liut in many [)aits of the world it seems as- 
if the old shore-lini's. which once marked the limit of these for- 
mations, were not very well developed or easily recognized. It 
■ . *.Prom the Proceedings of the Boston 8t)ciety of NMural History, 
vol. XXV. Awarded the tir^t of the annual Walker prizes of tlie So- 
ciety for the year Ihirj. 
