104  PRE-CAMBKIAN    GEOLOGY   OF    NORTH   AMERICA. 
"  zoic  "  basis  and  that  therefore  terms  such  as  Archean  and  Algon- 
kian  are  desirable  to  indicate  the  physical  classification. 
Daly,45  in  1908,  from  a  consideration  of  the  origin  of  augite  andes- 
ite  and  of  related  ultra-basic  rocks,  suggests  that  basaltic  magma 
forms  the  universal  substratum  of  the  earth's  crust  to-day  and  has 
formed  that  substratum  since  Keewatin  time;  that  this  basaltic  sub- 
stratum is  stratified  by  density  so  that  the  lower  layer  of  the  crust  is 
crystallized  basaltic  magma  and  the  upper  layer  is  dominantly  acidic. 
The  fundamental  gneiss  of  the  pre-Cambrian  was  crystallized  in  pre- 
Keewatin  time  and  through  it  the  basic  Keewatin  lavas  were  erupted. 
By  the  spontaneous  differentiation  of  the  primary  basalt  through 
fractional  crystallization,  the  few  rock  types  specially  discussed  in 
this  paper  have  been  locally  derived.  Most  of  the  other  eruptive 
rocks  are,  on  this  same  working  hypothesis,  regarded  as  derived  from 
the  formation  and  differentiation  of  magmas  which  are  the  product 
of  the  solution  of  the  acidic  original  gneissic  shell  and  of  its  sedi- 
mentary  veneer  in  the  primary  basalt. 
NOTES. 
1  Observations  on  the  geology  of  the  United  States  explanatory  of  a  geological 
map,  by  Win.  Maclure.  Trans.  Am.  Philos.  Soc,  vol.  6,  1809,  pp.  411-428, 
with  map. 
2  Geological  text-book,  for  aiding  the  study  of  North  American  geology,  by 
Amos  Eaton.     2d  ed.,  Albany,  New  York,  and  Troy,  1832,  pp.  134. 
3American  geology,  by  Ebenezer  Emmons.  Albany,  1855,  pp.  194,  251,  with 
atlas  and  geological  map  of  United  States. 
4  Esqnisse  geologique  du  Canada,  a  l'Exposition  Universelle  de  Paris,  by  W.  E. 
Logan  and  T.  Sterry  Hunt.  Paris,  1855,  pp.  100,  with  geological  map.  From 
translation  by  Robert  Stein. 
5  Manual  of  geology,  by  James  D.  Dana.  1st  ed.,  Philadelphia,  1863,  pp.  798, 
with  map. 
6  On  the  occurrence  of  organic  remains  in  the  Laurentian  rocks  of  Canada, 
by  W.  E.  Logan.     Quart.  Jour.  Geol.  Soc.  London,  vol.  21,  1865,  pp.  45-50. 
7  Esquisse  geologique  du  Canada,  suivie  d'un  Catalogue  descriptif  de  la  collec- 
tion de  cartes  et  coupes  geologiques,  livres  imprimes,  roches,  fossiles  et  ruine- 
raux  economiques  envoyee  a  l'Exposition  Universelle  de  1867,  by  T.  Sterry  Hunt. 
Paris,  1867,  pp.  72.     From  translation  by  Robert  Stein. 
8  Notice  of  the  address  of  Prof.  T.  Sterry  Hunt  before  the  American  Associa- 
tion at  Indianapolis,  by  James  D.  Dana.  Am.  Jour.  Sci.,  3d  ser.,  vol.  3,  1872, 
pp.  86-93;  vol.  4,  1S72,  pp.  97-105. 
"Manual  of  geology,  by  James  D.  Dana.  2d  ed.,  New  York,  1S76,  pp.  828, 
with  map. 
10  Systematic  geology,  by  Clarence  King.  U.  S.  Geol.  Explor.  40th  Par.,  vol. 
1,  1878,  pp.  803,  12  analytical  geological  maps,  accompanied  by  geological  and 
topographical  atlas. 
"Report  of  observations  on  the  stratigraphy  of  the  Quebec  group,  and  the 
older  crystalline  rocks  of  Canada,  by  A.  R.  C.  Selwyn.  Rept.  Prog.  Geol. 
Survey  Canada  for  1877-78,  1879,  pp.  1-15a. 
