﻿4 
  

  

  Harper: 
  A 
  week 
  in 
  eastern 
  Texas 
  291 
  

  

  the 
  state 
  into 
  eleven 
  regions 
  and 
  indicates 
  land 
  values 
  for 
  each 
  

   county 
  by 
  shading.* 
  

  

  Geological 
  and 
  climatic 
  relations, 
  — 
  From 
  Pennsylvania 
  to 
  

   Alabama 
  there 
  is 
  a 
  vast 
  geological 
  hiatus 
  at 
  the 
  fall-line, 
  between 
  

   the 
  metamorphic 
  rocks 
  of 
  the 
  Piedmont 
  region 
  (and 
  Triassic 
  

   sedimentary 
  strata 
  for 
  part 
  of 
  the 
  distance 
  across 
  North 
  Carolina) 
  

   and 
  the 
  unindurated 
  Cretaceou^ 
  and 
  later 
  strata 
  of 
  the 
  coastal 
  

   plain. 
  From 
  Alabama 
  to 
  Illinois 
  and 
  Oklahoma 
  the 
  coastal 
  

   plain 
  formations 
  at 
  the 
  fall-line 
  abut 
  against 
  Paleozoic 
  strata, 
  

   which 
  although 
  mainly 
  horizontal 
  and 
  unaltered 
  are 
  characterized 
  

   by 
  an 
  abundance 
  of 
  hard 
  rock, 
  something 
  that 
  is 
  relatively 
  scarce 
  

   in 
  the 
  coastal 
  plain. 
  In 
  Texas, 
  however, 
  the 
  fall-line 
  is 
  hard 
  to 
  

   define, 
  for 
  strata 
  of 
  Cretaceous 
  age 
  in 
  practically 
  uninterrupted 
  

  

  m 
  

  

  series 
  extend 
  from 
  the 
  unquestioned 
  coastal 
  plain 
  area 
  far 
  into 
  

   the 
  interior, 
  merging 
  into 
  the 
  southern 
  extremity 
  of 
  the 
  Great 
  

   Plains, 
  a 
  province 
  whose 
  rocks 
  are 
  itiostly 
  of 
  the 
  same 
  age 
  as 
  the 
  

   coastal 
  plain 
  strata, 
  but 
  nearly 
  as 
  hard 
  on 
  the 
  average 
  as 
  those 
  of 
  

   Paleozoic 
  age. 
  But 
  in 
  Texas 
  it 
  is 
  customar>^ 
  to 
  place 
  the 
  boun- 
  

   dary 
  of 
  the 
  coastal 
  plain 
  somewhat 
  arbitrarily 
  at 
  the 
  inland 
  edge 
  of 
  

   the 
  black 
  prairie 
  belt 
  (described 
  farther 
  on). 
  From 
  the 
  vicinity 
  

   of 
  Austin 
  southwestward 
  this 
  boundary 
  corresponds 
  pretty 
  closely 
  

   With 
  a 
  displacement 
  known 
  as 
  the 
  Balcones 
  fault, 
  which 
  marks 
  a 
  

   rather 
  abrupt 
  transition 
  from 
  the 
  undulating 
  black 
  prairie 
  to 
  the 
  

   rocky 
  hills 
  of 
  the 
  Edwards 
  Plateau. 
  

  

  As 
  in 
  Alabama, 
  Mississippi 
  and 
  Louisiana, 
  the 
  distribution 
  of 
  

   vegetation 
  and 
  other 
  biotic 
  features 
  in 
  Texas 
  can 
  be 
  correlated 
  

   pretty 
  well 
  with 
  geological 
  formations, 
  although 
  there 
  are 
  some 
  

   discrepancies 
  between 
  existing 
  geological 
  and 
  vegetation 
  maps, 
  

   which 
  however 
  may 
  diminish 
  with 
  the 
  progress 
  of 
  exploration. 
  

   But 
  in 
  Texas 
  one 
  encounters 
  an 
  environmental 
  factor 
  that 
  does 
  

   not 
  occur 
  in 
  the 
  coastal 
  plain 
  anywhere 
  farther 
  east 
  (except 
  to 
  a 
  

  

  ^ 
  • 
  • 
  - 
  _ 
  _ 
  _ 
  _ 
  

  

  degr 
  

  

  The 
  ISO- 
  

  

  hyetal 
  line 
  of 
  35 
  inches 
  annual 
  rainfall, 
  which 
  with 
  the 
  tem- 
  

   perature 
  prevailing 
  in 
  that 
  latitude 
  marks 
  approximately 
  the 
  

   transition 
  from 
  humid 
  to 
  semi-arid 
  conditions, 
  passes 
  through 
  or 
  

  

  * 
  A 
  review 
  of 
  this 
  by 
  F. 
  V. 
  Emerson 
  (Geog. 
  Review 
  2: 
  ^S^~:^Ss, 
  Nov. 
  1916) 
  

   reproduces 
  the 
  same 
  map, 
  and 
  may 
  be 
  more 
  accessible 
  to 
  some 
  readers. 
  

  

  