﻿GEOLOGY. 
  249 
  

  

  These 
  consist, 
  in 
  great 
  part, 
  of 
  that 
  description 
  of 
  rock 
  

   known 
  as 
  chert 
  or 
  hornstone, 
  an 
  impure 
  flint, 
  often 
  con- 
  

   taining, 
  or 
  bearing 
  the 
  impressions 
  of, 
  fossil 
  shells 
  or 
  

   corals, 
  but 
  most 
  usually 
  of 
  crinordeal 
  forms, 
  the 
  separate 
  

   joints 
  or 
  fragments 
  of 
  encrinital 
  stems, 
  the 
  latter 
  occur- 
  

   ring 
  frequently, 
  separate 
  from 
  the 
  matrix, 
  in 
  the 
  character 
  

   of 
  pebbles, 
  being 
  wholly 
  converted 
  into 
  the 
  same 
  cherty 
  

   rock, 
  or 
  into 
  a 
  yellowish 
  jasper, 
  and 
  in 
  some 
  instances, 
  

   into 
  Carnelian 
  or 
  Chalcedony. 
  

  

  Associated 
  with 
  these 
  are 
  found 
  the 
  quartz 
  rocks 
  in 
  

   various 
  modifications, 
  as 
  ferruginous, 
  milky, 
  and 
  limpid 
  

   quartz; 
  jaspers, 
  yellow, 
  red, 
  and 
  banded, 
  as 
  well 
  as 
  

   the 
  black 
  variety 
  known 
  as 
  Lydian 
  Stone 
  or 
  touch- 
  

   stone, 
  together 
  with 
  several 
  varieties 
  or 
  modifications 
  of 
  

   agates, 
  chalcedony, 
  and 
  carnelian. 
  

  

  Porphyry 
  has 
  been 
  occasionally 
  seen, 
  but 
  is 
  rare. 
  

   Among 
  these 
  are 
  also 
  found 
  jietriflictions 
  of 
  coral, 
  

   shell, 
  and 
  wood 
  in 
  rare 
  and 
  varied 
  conditions 
  of 
  mineral- 
  

   ization, 
  not 
  merely 
  silicified 
  in 
  the 
  simple 
  state, 
  as 
  ordi- 
  

   narily 
  seen, 
  but 
  often 
  agatized, 
  opalized, 
  and 
  converted 
  

   into 
  carnelian, 
  jasper, 
  and 
  jet. 
  

  

  As 
  every 
  particular 
  regarding 
  the 
  character 
  and 
  com- 
  

   position 
  of 
  the 
  drift 
  seems 
  to 
  be 
  a 
  desideratum, 
  it 
  may 
  

   not 
  perhaps 
  be 
  amiss 
  to 
  be 
  more 
  minute 
  in 
  these 
  details. 
  

   The 
  chert 
  and 
  jasper 
  pebbles, 
  without 
  possessing 
  any 
  

   very 
  marked 
  or 
  determinate 
  forms, 
  are 
  neither 
  distinctly 
  

   angular 
  nor 
  much 
  rounded, 
  although 
  palpably 
  water- 
  

   worn; 
  the 
  black 
  variety, 
  or 
  Lydian 
  Stone, 
  is 
  an 
  exception, 
  

   however, 
  being 
  generally 
  somewhat 
  flattened 
  with 
  rather 
  

   smooth 
  faces, 
  but 
  otherwise 
  irregular 
  in 
  outline. 
  

  

  The 
  larger 
  and 
  coarser 
  quartzose 
  and 
  jaspery 
  agates, 
  

   and, 
  in 
  rather 
  less 
  degree, 
  the 
  carnelians, 
  are 
  variously 
  

   contorted, 
  the 
  agates 
  frequently 
  of 
  rough 
  exterior, 
  and 
  

   many 
  of 
  both 
  cellular. 
  

  

  