82  CONTRIBUTIONS   TO   ECONOMIC    GEOLOGY,   1907,   PART   II. 
sufficiently  sandy  and  hard  to  form  a  conspicuous  ridge.  This  forma- 
tion is  particularly  well  exposed  as  a  ridge  along  the  western  side  of 
T.  5  N.,  R.  17  E.,  and  crosses  Fish  Creek  at  the  George  Moore  ranch. 
A  mile  farther  north  it  swings  to  the  west  and  can  be  traced  readily 
all  the  way  to  Lennep.  A  peculiarity  of  this  formation  is  its  general 
reddish  color  and  the  occurrence  of  a  layer  of  red,  sandy,  cannon- 
ball  nodules  near  the  middle.  Its  age  has  not  been  definitely 
determined,  but  lithologically  it  belongs  to  the  overlying  formation 
and  hence  it  will  be  provisionally  regarded  as  a  part  of  the  Laramie. 
Taken  as  a  whole,  the  upper  part  of  the  Laramie  formation  is 
distinguished  from  the  formations  above  and  below  by  its  light-gray 
color  in  comparison  with  their  somber  hues.  It  is  composed  largely 
of  soft  gray  sandstone  and  variegated  shale.  The  gray  beds,  from 
1,000  to  2,400  feet  thick,  make  a  conspicuous  valley  across  the 
middle  of  T.  6  N.,  Rs.  13  to  16  E.  As  a  whole  the  formation  weathers 
so  readily  that  it  normally  forms  low  country,  and  for  some  miles  in 
this  area  it  coincides  with  the  valley  of  Fish  Creek.  The  gray  beds 
of  the  Laramie  formation  are  overlain,  possibly  with  unconformity, 
by  somber-colored  sandstone  and  shale  which  may  represent  the 
Livingston  formation.  Sufficient  paleontologic  evidence  has  not 
been  obtained,  however,  to  determine  the  limits  of  these  stratigraphic 
units.  A  section  measured  by  C.  A.  Fisher  and  T.  W.  Stanton  on 
a  fork  of  Big  Elk  Creek  gives  a  thickness  of  5,592  feet  from  the  base 
of  the  Laramie  to  the  base  of  the  sandstone  and  grit  of  probable 
Fort  Union  age,  and  of  10,324  feet  for  the  beds  above  the  Bearpaw 
shale.  Further  field  work  is  necessary  before  the  lithologic  and 
paleontologic  distinctions  of  the  Laramie  and  Livingston  formations 
can  be  determined. 
The  Fort  Union  formation,  of  unknown  thickness,  but  exceeding 
4,300  feet,  is  the  youngest  in  this  area.  It  is  composed  largely  of 
sandstone,  alternating  with  shale.  The  base  of  the  formation  is  a 
particularly  massive,  coarse-grained  sandstone  which  forms  pro- 
nounced wooded  ridges.  Fort  Union  beds  underlie  the  southern  part 
of  T.  6  N.,  Rs.  12  to  16  E.,  and  compose  the  north  and  east  bases,  at 
least,  of  the  Crazy  Mountains. 
The  character,  distribution,  and  thickness  of  the  above-described 
formations  will  be  discussed  much  more  fully  in  a  report  now  in 
preparation  by  L.  H.  Woolsey  and  the  writer. 
IGNEOUS  ROCKS. 
Surrounding  the  Crazy  Mountains,  which  are  formed  by  diorite 
stocks  breaking  through  a  basin  of  sedimentary  rocks,  is  a  zone  of 
igneous  intrusions.  These  occur  as  dikes,  sheets,  and  laccoliths  and 
were  probably  injected  at  the  time  of  the  folding  to  which  the  rocks 
of  this  area  have  been  subjected.     The  most  noticeable  occurrences 
