﻿II] 
  General 
  Geology 
  : 
  Grand 
  Gulf 
  Oligocene 
  95 
  

  

  Grand 
  Gulf, 
  traced 
  it 
  from 
  Sicily 
  Island 
  to 
  the 
  falls 
  at 
  Alexandria 
  

   and 
  correlated 
  it 
  with 
  the 
  bluffs 
  on 
  the 
  east 
  side 
  of 
  the 
  Missis- 
  

   sippi 
  " 
  above 
  Natchez. 
  "* 
  In 
  1869, 
  Hilgard 
  skirted 
  the 
  southern 
  

   boundary 
  of 
  the 
  formation, 
  passed 
  across 
  the 
  same 
  in 
  Calcasieu 
  

   and 
  Vernon 
  parishes 
  and 
  examined 
  the 
  northern 
  escarpment 
  on 
  

   Bayou 
  Toro 
  and 
  between 
  Little 
  river 
  and 
  Harrisonburg. 
  During 
  

   1869 
  and 
  70, 
  Hopkins 
  made 
  several 
  trips 
  across 
  the 
  State 
  seeing 
  

   the 
  Grand 
  Gulf 
  at 
  several 
  points. 
  His 
  descriptions 
  of 
  the 
  Grand 
  

   Gulf 
  in 
  Louisiana 
  are 
  the 
  most 
  complete 
  that 
  have 
  yet 
  been 
  

  

  published. 
  t 
  

  

  Johnson 
  X 
  and 
  Lerch 
  || 
  have 
  both 
  examined 
  portions 
  of 
  the 
  

   northern 
  boundary 
  between 
  Lena 
  and 
  Harrisonburg. 
  

  

  Features 
  of 
  the 
  Formation 
  

  

  Characteristics. 
  — 
  This 
  formation, 
  which 
  unconformably 
  over- 
  

   lies 
  the 
  Vicksburg,§ 
  consists 
  in 
  the 
  northern 
  part 
  of 
  its 
  territory, 
  

   of 
  a 
  series 
  of 
  light 
  colored 
  sandstones 
  and 
  claystones 
  of 
  white, 
  

   gray, 
  or 
  yellowish 
  gray 
  tints. 
  The 
  sandstone 
  is 
  generally 
  

   rather 
  soft, 
  never 
  over 
  20 
  feet 
  in 
  thickness 
  usually 
  only 
  three 
  or 
  

   four. 
  Beds 
  of 
  loose 
  sand 
  are 
  unusual. 
  The 
  sand 
  grains 
  are 
  

   commonly 
  quite 
  sharp. 
  The 
  hardness 
  of 
  the 
  sandstone 
  in 
  a 
  

   given 
  layer 
  varies 
  very 
  greatly 
  and 
  makes 
  quarrying 
  in 
  this 
  

   rock 
  a 
  rather 
  uncertain 
  business. 
  Beds 
  of 
  sand 
  will 
  

   pass 
  in 
  a 
  few 
  feet 
  horizontally 
  into 
  hard 
  sandstones. 
  The 
  

   accompanying 
  plate 
  shows 
  an 
  exposure 
  of 
  Grand 
  Gulf 
  in 
  a 
  

   cut 
  on 
  the 
  Texas 
  and 
  Pacific 
  railroad, 
  about 
  three 
  miles 
  

   west 
  of 
  Lena. 
  The 
  lower 
  sandstone 
  bed 
  in 
  this 
  exposure 
  

   is 
  rather 
  uniform. 
  The 
  upper 
  irregular 
  one 
  shows 
  on 
  a 
  small 
  

   scale 
  the 
  nodular 
  masses 
  in 
  which 
  the 
  sandstone 
  occurs. 
  In 
  

   some 
  cases 
  the 
  amount 
  of 
  silicious 
  cement 
  is 
  so 
  great 
  that 
  the 
  

   rock 
  resembles 
  a 
  quartzite. 
  Such 
  is 
  the 
  typical 
  Grand 
  Gulf 
  

  

  * 
  A 
  Geog. 
  Des. 
  of 
  the 
  State 
  of 
  Louisiana 
  by 
  William 
  Darby, 
  1816, 
  pp. 
  45- 
  

   46. 
  

  

  t 
  ist 
  An. 
  Repl. 
  Geol. 
  Surv. 
  La., 
  1S70, 
  pp. 
  98-102 
  ; 
  2d 
  An. 
  Kept. 
  Geol. 
  

   Surv. 
  La., 
  187 
  1, 
  pp. 
  18-26. 
  

  

  X 
  50th 
  Cong, 
  ist 
  Sess., 
  House 
  Ex. 
  Doc, 
  vol. 
  26, 
  No. 
  195, 
  pp. 
  13-14, 
  1888. 
  

  

  I] 
  Bull. 
  La. 
  Expt. 
  Stations 
  ; 
  Geol. 
  and 
  Agr., 
  part 
  II, 
  1893, 
  pp. 
  93-98. 
  

  

  § 
  Hilgard.— 
  The 
  Later 
  Tertiary 
  of 
  the 
  Gulf 
  of 
  Mexico. 
  Am. 
  Jour. 
  Sci., 
  

   vol. 
  22, 
  1881, 
  pp. 
  58-65. 
  

  

  