﻿280 
  REPORT 
  UNITED 
  STATES 
  ENTOMOLOGICAL 
  COMMISSION. 
  

  

  tween 
  the 
  Mobrara 
  and 
  White 
  Eivers, 
  and 
  the 
  sand 
  hills 
  on 
  the 
  latter 
  

   stream, 
  form 
  the 
  only 
  exceptions 
  worthy 
  of 
  note, 
  and 
  indeed 
  it 
  is 
  doubt- 
  

   ful 
  whether 
  they 
  should 
  be 
  excepted. 
  The 
  Llano 
  Estacado 
  is 
  mainly 
  

   covered 
  with 
  fine 
  grass, 
  while 
  Jornada 
  del 
  Muerto, 
  of 
  New 
  Mexico, 
  de- 
  

   rives 
  its 
  name, 
  not 
  from 
  having 
  the 
  characteristics 
  of 
  a 
  desert, 
  but 
  

   solely 
  from 
  the 
  dearth 
  of 
  water. 
  

  

  The 
  Black 
  Hills 
  are 
  an 
  isolated 
  group 
  of 
  mountains, 
  some 
  75 
  miles 
  in 
  

   length 
  by 
  50 
  in 
  breadth, 
  rising 
  to 
  a 
  height 
  of 
  6,000 
  to 
  7,000 
  feet 
  above 
  

   the 
  sea, 
  and 
  about 
  3,000 
  feet 
  above 
  the 
  surrounding 
  level. 
  They 
  are 
  

   heavily 
  timbered 
  throughout, 
  while 
  about 
  their 
  base 
  the 
  grasses 
  are 
  

   everywhere 
  luxuriant. 
  

  

  The 
  Mountain 
  Area. 
  

  

  With 
  regard 
  to 
  the 
  Eocky 
  Mountain 
  region 
  of 
  British 
  America, 
  it 
  may 
  

   be 
  briefly 
  dismissed, 
  as 
  little 
  is 
  known 
  about 
  it 
  in 
  detail. 
  It 
  is 
  essen- 
  

   tially 
  a 
  heavily 
  timbered 
  region. 
  It 
  is 
  made, 
  up 
  of 
  a 
  number 
  of 
  ranges 
  

   trending 
  parallel 
  to 
  one 
  another 
  and 
  separated 
  by 
  narrow 
  valleys. 
  It 
  

   is 
  a 
  region 
  of 
  heavy 
  rainfall 
  and 
  slight 
  evaporation 
  ; 
  and 
  not 
  only 
  the 
  

   mountains 
  but 
  the 
  valleys 
  also 
  are 
  covered 
  with 
  forests. 
  

  

  Within 
  the 
  Western 
  United 
  States 
  the 
  presence 
  or 
  absence, 
  and 
  even 
  

   the 
  comparative 
  density 
  and 
  the 
  prevalent 
  species, 
  of 
  the 
  forests 
  may 
  be 
  

   predicted 
  with 
  a 
  reasonable 
  degree 
  of 
  certainty 
  and 
  detail 
  from 
  the 
  lati- 
  

   tude 
  and 
  elevation, 
  i. 
  e., 
  from 
  the 
  same 
  elements 
  as 
  there 
  determine 
  the 
  

   degree 
  of 
  moisture 
  of 
  the 
  climate. 
  Excepting 
  in 
  the 
  northern 
  part 
  of 
  

   Idaho, 
  Washington, 
  Montana, 
  and 
  Wyoming, 
  the 
  general 
  level 
  of 
  the 
  

   country 
  is 
  not 
  sufficiently 
  elevated 
  to 
  cover 
  it 
  with 
  forests, 
  and 
  conse- 
  

   quently 
  they 
  are, 
  except 
  in 
  the 
  localities 
  summarized 
  above, 
  confined 
  

   to 
  mountain 
  ranges 
  and 
  high 
  plateaus. 
  In 
  southern 
  latitudes, 
  even, 
  many 
  

   ranges 
  of 
  considerable 
  altitude 
  are 
  not 
  sufficiently 
  high 
  to 
  reach 
  the 
  

   lower 
  level 
  of 
  timber, 
  as 
  in 
  the 
  case 
  of 
  the 
  majority 
  of 
  the 
  ranges 
  in 
  

   Nevada, 
  Arizona, 
  and 
  Southern 
  California. 
  

  

  Occupying 
  the 
  next 
  zone 
  below 
  the 
  forests, 
  we 
  find 
  the 
  grasses. 
  They 
  

   are 
  found 
  on 
  the 
  foothills 
  of 
  the 
  mountains 
  and 
  the 
  margins 
  of 
  the 
  val- 
  

   leys, 
  and, 
  in 
  cases 
  where 
  the 
  elevation 
  and 
  latitude 
  are 
  sufficiently 
  high 
  

   to 
  insure 
  moisture 
  enough, 
  covering 
  the 
  valleys. 
  In 
  other 
  cases 
  a 
  zone 
  

   of 
  sage 
  succeeds, 
  the 
  two 
  growths 
  grading 
  into 
  one 
  another, 
  and 
  this 
  in 
  

   turn 
  in 
  the 
  most 
  arid 
  localities, 
  as 
  in 
  the 
  deserts 
  of 
  Utah, 
  Nevada, 
  and 
  

   Southern 
  California, 
  is 
  succeeded 
  by 
  scanty 
  growth 
  of 
  cacti, 
  yucca, 
  and 
  

   by 
  naked 
  soil 
  without 
  vegetation. 
  This 
  successiou, 
  being 
  a 
  direct 
  result 
  

   of 
  the 
  conditions 
  of 
  aridity, 
  can 
  be 
  premised 
  regarding 
  a 
  certain 
  region 
  

   with 
  considerable 
  certainty. 
  

  

  The 
  more 
  northern 
  section 
  of 
  the 
  Eocky 
  Mountains 
  in 
  the 
  United 
  

   States, 
  including 
  the 
  mountain 
  region 
  of 
  Montana, 
  Idaho, 
  and 
  Wyom- 
  

   ing, 
  is 
  characterized, 
  in 
  the 
  northern 
  part, 
  by 
  a 
  tolerably 
  great 
  precipi- 
  

   tation, 
  allowing 
  a 
  growth 
  of 
  forests 
  almost 
  as 
  great 
  as 
  in 
  the 
  British 
  

   Possessions. 
  The 
  whole 
  of 
  Kootenai 
  County, 
  Idaho, 
  is 
  covered 
  by 
  

  

  