SUMMARY   OF   GENERAL   LITERATURE.  73 
the  north  shore  of  Lake  Huron  composed  of  slates,  conglomerates, 
quartzites,  layers  of  jasper,  and  chert,  with  quartz  and  jasper  con- 
glomerates, limestones,  and  beds  of  diorite  which  graduate  into  syenite 
or  epidote,  and  also  other  areas  which  have  been  placed  as  the  equiva- 
lent of  this  series  on  lithological  grounds. 
King,10  in  1878,  states  that  in  the  Archean  outcrops  of  the  fortieth 
parallel  one  can  not  fail  to  notice  the  widespread  simplicity  of  peno- 
logical forms,  the  prevalence  of  granites,  granitoid  gneisses,  and  dio- 
ritic  metamorphic  rocks,  the  paucity  of  argillites,  quartzites,  lime- 
stones, and  zirconiferous  and  staurolitic  schists,  the  infrequence  of 
large  bodies  of  magnetic,  specular,  or  spathic  iron,  and  the  complete 
absence  of  corundum,  chrysolite,  serpentine,  steatite,  pyroxene  rocks, 
the  true  nacreous  schists,  and  other  minor  forms  observed  in  the 
Appalachian  system. 
Without  doubt,  the  most  interesting  facts  which  the  comparison  of 
these  exposures  discloses  are:  When  considered  in  depth,  from  the 
uppermost  limits  of  our  so-called  Huronian  to  the  lowest  Laurentian 
exposure,  there  is,  first,  a  regular,  steady  increase  of  the  intensity  of 
metamorphism,  and,  second,  a  pretty  regular  increase  in  the  thick- 
ness of  individual  members  of  the  series.  The  lowest  Laurentian 
aplitic  granitoid  bodies  of  the  Laramie  Hills  are  the  heaviest  beds 
and  the  most  changed  from  their  original  sedimentary  condition. 
The  higher  Huronian  group  of  gneisses,  quartzites,  conglomerates, 
dolomites,  and  argillites  are  at  once  the  most  thinly  bedded  and  least 
metamorphosed.  Individual  beds  remain  as  specialized  as  the  day 
they  were  deposited.  At  the  lower  exposures  of  the  whole  Archean 
formation  well-defined  crystals  are  of  great  rarity;  even  microscopic 
apatite,  the  best  presented  species,  is  generally  crushed  and  dislo- 
cated; micas  are  distorted,  and  all  feldspars  are  more  or  less  frag- 
mentary. A  marked  contrast  is  observable  at  the  upper  extreme; 
here  many  micas,  hornblendes,  garnets,  and  even  feldspars  are  nearly.' 
if  not  quite,  completed  crystals.  The  exceptions  to  this  are  those 
places,  already  described,  where  local  compression  has  broken  up  the 
original  arrangement  of  the  crystalline  ingredients. 
Nearly  every  considerable  mountain  body  between  the  Wasatch  and 
the  California  line  shows  in  the  lowest  horizons  exposures  of  one  or 
more  bodies  of  granite.  These  are  classified  into  four  groups  on 
penological  grounds.  The  first  type  consists  of  quartz,  orthoclase,  an 
unimportant  amount  of  plagioclase,  and  muscovite,  with  a  small 
quantity  of  microscopic  apatite.  These  are  all  Avest  of  Reese  River, 
longitude  117°.  They  are  all  associated  with  the  Nevada  type  of 
Archean  crystalline  schists,  composed  of  quartz,  biotite,  muscovite, 
and  magnetite,  or  quartz,  hornblende,  and  magnetite.  As  to  the  age 
of  the  granites  of  this  type  there  are  practically  no  data  available. 
At  one  place  it  is  intimately  involved  with  the  crystalline  schists  and 
