﻿10 
  G. 
  II. 
  Stone 
  — 
  Glaciation 
  of 
  Central 
  Idaho. 
  

  

  form 
  a 
  confluent 
  ice 
  sheet 
  in 
  each 
  valley. 
  The 
  ice 
  covered 
  all 
  

   the 
  lower 
  hills 
  in 
  the 
  central 
  parts 
  of 
  each 
  drainage 
  basin 
  and 
  

   flowed 
  westward 
  up 
  and 
  over 
  these 
  hills, 
  and 
  Anally 
  narrowed 
  

   into 
  the 
  deep 
  canons 
  which 
  form 
  the 
  channels 
  of 
  the 
  South 
  

   and 
  Middle 
  Forks 
  at 
  and 
  below 
  3,500 
  feet 
  elevation. 
  The 
  

   great 
  ice 
  sheet 
  which 
  at 
  one 
  time 
  covered 
  British 
  Columbia 
  

   east 
  of 
  the 
  Cascade 
  range, 
  and 
  which 
  had 
  a 
  southward 
  flow 
  

   during 
  the 
  time 
  of 
  deepest 
  ice, 
  did 
  not 
  reach 
  so 
  far 
  south 
  as 
  

   the 
  Clearwater 
  valley. 
  The 
  valley 
  ice 
  sheets 
  of 
  the 
  South 
  and 
  

   Middle 
  Forks 
  of 
  the 
  Clearwater 
  closely 
  correspond 
  to 
  what 
  

   Russell 
  has 
  termed 
  the 
  Piedmont 
  type 
  of 
  glaciers. 
  

  

  The 
  signs 
  of 
  glaciation 
  in 
  all 
  the 
  region 
  in 
  question 
  are 
  dis- 
  

   tinct 
  and 
  unmistakable. 
  Morainal 
  ridges 
  and 
  terraces 
  are 
  com- 
  

   mon 
  in 
  the 
  higher 
  valleys, 
  but 
  in 
  general 
  the 
  ice 
  appears 
  to 
  

   have 
  retreated 
  at 
  so 
  uniform 
  a 
  rate 
  as 
  to 
  leave 
  most 
  of 
  the 
  

   morainal 
  matter 
  in 
  the 
  form 
  of 
  a 
  diffused 
  sheet. 
  There 
  are 
  

   numerous 
  lakes 
  held 
  in 
  by 
  morainal 
  dams, 
  as 
  the 
  Lower 
  

   Payette 
  Lake 
  and 
  Trout 
  Lake 
  on 
  Lake 
  Creek, 
  a 
  few 
  miles 
  

   southeast 
  from 
  Buffalo 
  Hump. 
  Only 
  in 
  few 
  regions 
  do 
  the 
  

   rocks 
  withstand 
  weathering 
  so 
  as 
  to 
  preserve 
  the 
  glacial 
  

   scratches. 
  At 
  Buffalo 
  Hump 
  the 
  granites, 
  schists, 
  and 
  quartz- 
  

   ites 
  equal 
  or 
  surpass 
  the 
  best 
  Maine 
  and 
  New 
  Hampshire 
  gran- 
  

   ite 
  in 
  capacity 
  to 
  withstand 
  the 
  elements, 
  and 
  the 
  rock 
  is 
  

   beautifully 
  smoothed 
  and 
  scored 
  to 
  within 
  about 
  thirty 
  feet 
  

   below 
  the 
  summit 
  of 
  the 
  Hump. 
  The 
  glaciated 
  stones 
  are 
  in 
  

   general 
  so 
  smooth 
  and 
  rounded 
  at 
  the 
  angles 
  that 
  they 
  have 
  

   often 
  been 
  mistaken 
  for 
  water-rolled 
  stones, 
  distinct 
  scratches 
  

   being 
  rare. 
  In 
  the 
  regions 
  where 
  the 
  granite 
  and 
  schists 
  

   weather 
  readily, 
  the 
  morainal 
  matter 
  consists 
  of 
  smoothed 
  stones 
  

   of 
  quartzite 
  or 
  other 
  resistant 
  rocks, 
  scattered 
  through 
  angular 
  

   sand 
  and 
  gravel 
  resulting 
  from 
  the 
  disintegration 
  of 
  the 
  frag- 
  

   ments 
  of 
  granite 
  and 
  schists. 
  In 
  many 
  cases 
  the 
  glaciated 
  

   stones 
  are 
  remarkably 
  round 
  and 
  smooth 
  almost 
  to 
  the 
  tops 
  of 
  

   ridges 
  from 
  which 
  the 
  ice 
  flowed 
  in 
  opposite 
  directions, 
  as 
  on. 
  

   Buffalo 
  Hump 
  and 
  on 
  the 
  much 
  dissected 
  ridge 
  dividing 
  Boise 
  

   Basin 
  from 
  the 
  valley 
  of 
  the 
  South 
  Fork 
  of 
  the 
  Payette. 
  

   Much, 
  perhaps 
  most 
  of 
  the 
  morainal 
  matter 
  was 
  sub-glacial, 
  

   which 
  accounts 
  for 
  the 
  great 
  attrition 
  it 
  received. 
  

  

  The 
  water-transported 
  deposits 
  of 
  the 
  glaciers 
  of 
  this 
  region 
  

   were 
  mostly 
  "overwash," 
  i. 
  e., 
  were 
  sediments 
  poured 
  out 
  of 
  

   ice 
  channels 
  into 
  open 
  ground 
  beyond 
  the 
  front 
  of 
  the 
  ice. 
  

   These 
  are 
  sometimes 
  plain-like, 
  as 
  at 
  Warren 
  Meadows; 
  at 
  other 
  

   times 
  they 
  take 
  the 
  form 
  of 
  terraces 
  in 
  the 
  narrow 
  valleys. 
  

   The 
  overwashed 
  gravels 
  have 
  often 
  been 
  regarded 
  as 
  lake 
  beds, 
  

   especially 
  when 
  they 
  expand 
  into 
  broad 
  plains. 
  Not 
  seldom 
  

   sediments 
  were 
  deposited 
  in 
  the 
  beds 
  of 
  streams 
  and 
  lakes 
  

   between 
  the 
  margin 
  of 
  the 
  ice 
  and 
  adjacent 
  hills. 
  The 
  Payette 
  

  

  