﻿Lane 
  — 
  Geothermal 
  Gradient 
  in 
  Michigan. 
  435 
  

  

  higher 
  gradient, 
  but 
  the 
  chances 
  are 
  it 
  was 
  taken 
  with 
  a 
  ther- 
  

   mometer 
  not 
  reliable, 
  and 
  perhaps 
  before 
  the 
  heat 
  of 
  drilling 
  

   had 
  been 
  dissipated. 
  In 
  case 
  of 
  the 
  Bay 
  City 
  well 
  the 
  well 
  

   had 
  been 
  idle 
  from 
  January 
  18 
  to 
  April 
  13, 
  1900, 
  the 
  elate 
  of 
  

   the 
  tests, 
  and 
  had 
  gradually 
  tilled 
  with 
  a 
  strong 
  heavy 
  brine 
  

   which 
  was 
  slowly 
  leaking 
  in 
  from 
  the 
  bottom 
  measures 
  when 
  

   they 
  stopped. 
  

  

  At 
  Alpena 
  flowing 
  wells 
  drawing 
  their 
  supplies, 
  probably, 
  

   mainly 
  at 
  698 
  to 
  Til 
  feet, 
  and 
  certainly 
  below 
  588 
  feet, 
  

   have 
  a 
  temperature 
  of 
  53°. 
  The 
  mean 
  surface 
  temperature 
  

   is 
  about 
  42°, 
  and 
  the 
  gradient 
  about 
  the 
  same. 
  

  

  At 
  Frankfort 
  two 
  wells 
  with 
  strong 
  flows 
  giving 
  off 
  H 
  2 
  S 
  

   freely, 
  the 
  one 
  2,200, 
  the 
  other 
  1,800 
  feet 
  deep, 
  have 
  tem- 
  

   peratures 
  of 
  56° 
  and 
  54° 
  F. 
  respectively, 
  but 
  the 
  water 
  is 
  said 
  

   to 
  come 
  in 
  about 
  800 
  feet 
  down. 
  There 
  are 
  reasons 
  for 
  believ- 
  

   ing 
  that 
  the 
  water 
  comes 
  from 
  the 
  Corniferons, 
  and 
  it 
  is 
  pretty 
  

   certainly 
  not 
  from 
  the 
  drift 
  and 
  must 
  come 
  more 
  than 
  570 
  feet 
  

   down. 
  The 
  mean 
  annual 
  temperature 
  is 
  about 
  44°, 
  so 
  that 
  the 
  

   gradient 
  is 
  a 
  little 
  less 
  than 
  heretofore, 
  probably 
  about 
  1° 
  in 
  

   80 
  feet. 
  

  

  The 
  gradient 
  thus 
  indicated 
  is 
  much 
  lower 
  than 
  that 
  found 
  

   by 
  Darton, 
  but 
  quite 
  comparable 
  with 
  those 
  found 
  by 
  W. 
  

   Hallock 
  in 
  the 
  Wheeling 
  boring 
  in 
  similar 
  strata. 
  

  

  2. 
  If, 
  however, 
  we 
  turn 
  to 
  the 
  Upper 
  Peninsula 
  we 
  have 
  a 
  

   region 
  notorious 
  for 
  its 
  low 
  thermal 
  gradient. 
  I 
  will 
  not 
  try 
  

   to 
  summarize 
  all 
  the 
  data 
  collected 
  by 
  Wheeler, 
  Agassiz 
  and 
  

   others, 
  but 
  merely 
  say 
  that 
  around 
  Calumet 
  from 
  a 
  mean 
  sur- 
  

   face 
  temperature 
  of 
  40° 
  F. 
  the 
  temperature 
  rises 
  to 
  about 
  

   84° 
  F. 
  at 
  4,400 
  feet, 
  almost 
  exactly 
  1° 
  F. 
  in 
  100 
  feet,* 
  This 
  

   gradient 
  is 
  probably 
  not 
  confined 
  to 
  the 
  Copper 
  Country. 
  

   Some 
  not 
  very 
  accurate 
  tests 
  which 
  I 
  made 
  in 
  the 
  Yulcan 
  Mine 
  

   on 
  the 
  Menominee 
  range 
  (with 
  a 
  cheap 
  thermometer, 
  after- 
  

   ward 
  compared 
  with 
  a 
  better) 
  gave 
  56° 
  at 
  a 
  depth 
  of 
  1,210 
  

   feet. 
  A 
  heavy 
  flow 
  of 
  water 
  (as 
  P. 
  Larrsen, 
  C. 
  E., 
  informed 
  

   me) 
  80 
  to 
  90 
  feet 
  below 
  surface 
  was 
  at 
  44° 
  F. 
  This 
  gives 
  a 
  

   gradient 
  of 
  1° 
  in 
  94 
  feet. 
  

  

  3. 
  The 
  causes 
  of 
  the 
  low 
  gradient 
  of 
  Keweenaw 
  Point 
  have 
  

   been 
  discussed, 
  and 
  various 
  explanations 
  of 
  variation 
  of 
  gradi- 
  

   ent 
  suggested, 
  at 
  which 
  we 
  will 
  glance, 
  although 
  I 
  do 
  not 
  think 
  

   we 
  can 
  decide 
  until 
  Darton 
  has 
  finished 
  his 
  work 
  upon 
  the 
  

   thermal 
  gradient 
  all 
  over 
  the 
  United 
  States, 
  which 
  is 
  the 
  most 
  

   pertinent. 
  We 
  may, 
  however, 
  throw 
  out 
  some 
  explanations 
  as 
  

   incorrect, 
  and 
  we 
  can 
  confirm 
  also 
  the 
  acute 
  observation 
  of 
  

   Darton 
  that 
  the 
  gradient 
  is 
  lowest 
  over 
  the 
  older 
  rock. 
  

  

  * 
  Any 
  data 
  widely 
  different 
  from 
  this 
  are 
  locally 
  affected 
  and 
  not 
  to 
  be 
  used. 
  

  

  