﻿292 
  E. 
  O. 
  Hovey 
  — 
  Acid 
  Dike 
  in 
  the 
  Triassic 
  area. 
  

  

  these 
  igneous 
  rocks 
  and 
  has 
  given 
  a 
  complete 
  series 
  of 
  refer- 
  

   ences 
  to 
  papers 
  dealing 
  with 
  their 
  mineralogical 
  and 
  their 
  

   chemical 
  composition, 
  to 
  which 
  the 
  reader 
  is 
  referred 
  for 
  any 
  

   further 
  details. 
  H. 
  D. 
  Campbell 
  and 
  W. 
  G. 
  Brown,* 
  how- 
  

   ever, 
  describe 
  petrographically 
  and 
  give 
  the 
  chemical 
  analyses 
  

   of 
  two 
  trap 
  rocks 
  from 
  the 
  Triassic 
  of 
  Culpeper 
  county, 
  Vir- 
  

   ginia, 
  which 
  depart 
  from 
  the 
  " 
  normal 
  diabase 
  " 
  of 
  Hawes 
  and 
  

   other 
  observers. 
  One 
  of 
  these 
  is 
  a 
  hypersthene-diabase 
  and 
  

   the 
  other 
  an 
  olivine-hypersthene-diabase. 
  Another 
  departure 
  

   from 
  the 
  monotonous 
  trap 
  has 
  been 
  reported 
  by 
  L. 
  S. 
  Gris- 
  

   wold,f 
  who 
  describes 
  a 
  very 
  basic 
  dike 
  consisting 
  essentially 
  of 
  

   augite, 
  hornblende 
  and 
  biotite, 
  with 
  almost 
  no 
  feldspar, 
  from 
  

   Beseck 
  Lake, 
  near 
  Bailey 
  ville, 
  Conn., 
  but 
  gives 
  no 
  chemical 
  

   analysis 
  of 
  the 
  rock. 
  The 
  three 
  instances 
  of 
  variation 
  just 
  

   cited 
  are 
  all 
  of 
  rocks 
  as 
  basic 
  as 
  or 
  more 
  basic 
  than 
  the 
  normal 
  

   or 
  average 
  diabase 
  of 
  the 
  Triassic 
  areas 
  mentioned. 
  The 
  dike 
  

   described 
  in 
  the 
  present 
  paper 
  is 
  the 
  first 
  one 
  to 
  be 
  recorded 
  

   from 
  these 
  areas 
  in 
  which 
  the 
  rock 
  is 
  acid 
  or 
  relatively 
  acid. 
  

  

  *Bull. 
  Geol. 
  Soc. 
  Amer 
  , 
  ii, 
  339-347, 
  1891. 
  

   f 
  Bull 
  Mus. 
  Comp. 
  Zool., 
  xvi, 
  239-242, 
  1893. 
  

  

  Am. 
  Mus. 
  Nat. 
  Hist 
  , 
  New 
  York, 
  Feb., 
  1897. 
  

  

  

  