508  PRE-CAMEJRIAN    ROCKS-  OF    NORTH    AMERICA.  [bull.  86. 
limestones.  Between  this  series  and  tile  Areheau  there  is  evidence  of 
a  great  physical  break,  although  the  two  are  in  apparent  conformity. 
The  series  in  one  section  rests  conformably  below  the  Olenellus  Cam- 
brian and  the  whole  is  regarded  by  Dawson  as  Cambrian,  but  as  terms 
are  used  in  this  paper  it  is  probably  in  part  or  in  whole  Upper  Algon- 
kian.  By  Dawson  the  series  is  compared'  with  the  Wasatch  Algonkian 
and  the  Chuar  and  Grand  canyon  series. 
THE   ADIRONDACK^. 
In  the  Adirondacks  is  a  core  of  gabbro  about  which  in  a  peripheral 
manner  is  a  great  series  of  regularly  bedded  gneisses,  quartz -schists, 
and  crystalline  limestones  which  are  often  ferruginous  or  graphitic.  At 
times  in  the  gneissic  series  are  beds  of  graphitic  schist  of  sufficient 
richness  to  serve  as  graphite  mines.  While  the  interior  structure  of 
the  rocks  of  this  series  now  shows  no  positive  clastic  characteristics, 
the  limestones,  graphitic  schists,  and  regularity  of  what  appears  to  be 
bedding  in  the  gneisses  leave  but  little  doubt  that  the  series  was  orig- 
inally clastic  and  belongs  with  the  Algonkian.  The  studies  of  Walcott 
render  it  probable  that  there  is  here  also  a  basal  complex,  and  along  the 
contact  Hues  of  the  series  Walcott  has  discovered  evidence  of  an  uncon- 
formity. This  Algonkian  is  so  remarkably  like  the  not  far  distant 
original  Upper  Laurentian  in  the  neighborhood  of  Ottawa  that  one 
can  not  doubt  that  the  two  are  or  once  were  continuous. 
OTHER  ALGONKIAN  AREAS. 
Besides  the  foregoing  list  of  areas  in  which  it  is  certain,  or  nearly 
certain,  that  there   are  Algonkian  rocks,  the   indefinite  knowledge 
available  of  many  other  districts  indicates  the  presence  of  series  which 
probably  fall  within  this  period.    In  much  of  the  work  in  the  West  the 
pre-Cambrian  rocks  are  treated  as  a   unit,  being  spoken  of  as  the  j 
metamorphic  group,  absolutely  no  attempt  being  made  to  treat  them 
upon  a  structural  basis.    This  was  natural  in  pioneer  work,  but  the 
fact  that  so  many  extensive  areas  of  pre-Cambrian  elastics  have  been  I 
discovered  in  districts  where  closer  work  has  been  done,  suggests  that  j 
in  the  future  there  will  be  discovered  many  new  series  of  pre-Cambrian  ] 
elastics.    The  most  extensive  areas  which  will  be  found  to  swell  this  ; 
system  will  doubtless  be  found  in  the  vast  stretches  of  pre-Cambrian 
rocks  of  Canada,  but  similar  series  may  be  found  in  central  New  Brans-  j 
wick,  in  Gaspe  peninsula,  in  the  Wind  river  and  Teton  ranges  of  Wyo-  | 
ming,  in  a  number  of  the  desert  ranges  of  Utah  and  Nevada,  in  South-  j 
era  California,  and  in  the  Appalachians.     In  this  last  and  most  difficult  j 
region,  the  recent  work  of  Prof.  Pumpelly's  corps  appears  to  indicate 
that  a  subdivision  of  the  pre-Cambrian  will  be  accomplished  in  Ver- 
mont, and  it  is  rather  probable  that  in  the  southern  Appalachians  arei 
areas  of  pre-Cambrian  elastics. 
