This  revolution  gave  to  North  America  nearly  its  present  outlines,
except  for  the  land  connections  with  Europe  and  Asia,  which  were

Digitized  by  VjUUVlt:


THE  TERTIARY  PERIOD


72s


Fig.  303.  —  Map  of  North  America  in  the  Tertiary  period.  Black  areas  =  known
exposures  of  marine  Tertiary;  white  aland;  lined  areas  =:  sea;  dotted  areas
«=  continental  formations  #


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Google


726  THE  TERTIARY  PERIOD

from  time  to  time  interrupted  and  renewed.  In  consequence  of
this,  marine  Tertiary  beds  occur  only  along  the  borders  of  the  con-
tinent, while  the  Tertiary  of  the  interior  is  all  of  continental  origin.
In  other  continents,  and  especially  in  Europe,  the  distribution  of
land  and  sea  waS  very  different  in  the  Tertiary  from  what  it  is
now,  and  the  topography  of  the  land  was  profoundly  altered  in
the  course  of  the  period.  Some  of  the  highest  mountain  ranges
of  the  earth  were  upheaved  in  Tertiary  times,  such  as  the  Atlas,
the  Alps,  the  Caucasus,  and  the  Himalayas,  and  many  ranges  of
earlier  date  were  subjected  to  renewed  compression  and  upheaval.
That  Tertiary  mountains  are  high*  is  not  due  to  any  extreme  de-
gree of  compression  as  compared  with  that  which  produced
older  ranges,  but  merely  to  the  youth  of  the  former;  denudation
has  not  yet  had  time  to  sweep  them  away.
The  Tertiary  system  or  period  is  divisible  into  five  well-distin-
guished series  or  epochs,  which  may  usually  be  identified  in  both
the  marine  and  continental  formations;  but  for  lack  of  common
fossils  .it  is  not  yet  possible  to  correlate  the  stages  and  substages
of  the  interior  region  with  those  of  the  coast.  In  the  preceding
table,  therefore,  no  exact  comparison  of  these  minor  subdivisions
is  intended.
