﻿IGNEOUS 
  ROCKS 
  AFTER 
  THEIR 
  CONSOLIDATION. 
  177 
  

  

  Bonney*, 
  the 
  late 
  Mr. 
  J. 
  A. 
  Phillips 
  f, 
  and 
  others 
  in 
  this 
  country 
  

   have 
  added 
  largely 
  to 
  our 
  knowledge 
  of 
  these 
  interestiug 
  processes. 
  

   To 
  Mr. 
  Van 
  Hise 
  we 
  are 
  indebted 
  for 
  the 
  further 
  very 
  important 
  

   discovery 
  that 
  not 
  only 
  portions 
  of 
  quartz-crystals, 
  but 
  fragments 
  

   derived 
  from 
  felspar- 
  J 
  and 
  hornblende- 
  § 
  individuals, 
  when 
  exposed 
  

   to 
  favourable 
  conditions, 
  undergo, 
  in 
  the 
  like 
  manner, 
  secondary 
  

   enlargement 
  ; 
  while 
  Professor 
  Bonney 
  has 
  shown 
  that 
  similar 
  en- 
  

   largements 
  of 
  biotite-fragments 
  often 
  take 
  place 
  during 
  a 
  develop- 
  

   ment 
  of 
  foliation 
  in 
  argillaceous 
  rocks 
  ||. 
  

  

  3. 
  Enlargement 
  of 
  Crystals 
  in 
  Igneous 
  Rocks. 
  

  

  That 
  the 
  crystals 
  of 
  many 
  eruptive 
  rocks 
  are 
  surrounded 
  by 
  

   irregular 
  outgrowths, 
  which 
  are 
  in 
  crystallographic 
  continuity 
  

   with 
  them, 
  and 
  appear 
  to 
  have 
  been 
  formed 
  subsequently 
  to 
  the 
  

   crystals 
  themselves, 
  has 
  been 
  recognized 
  by 
  many 
  authors, 
  such 
  as 
  

   C. 
  Hopfner 
  in 
  1881 
  % 
  ; 
  Prof. 
  G. 
  H. 
  Williams 
  in 
  1882 
  ** 
  ; 
  E. 
  Becke 
  f 
  f 
  , 
  

   K. 
  Bleibtreu 
  ±t, 
  and 
  E. 
  Hussak 
  in 
  1883 
  §§ 
  ; 
  by 
  Dolter 
  and 
  Hussak 
  in 
  

   1884 
  mi; 
  and 
  by 
  Dr. 
  Max 
  Koch 
  in 
  1887 
  ff. 
  These 
  authors, 
  however, 
  

   appear 
  to 
  have 
  generally 
  regarded 
  the 
  secondary 
  outgrowths 
  to 
  

   the 
  felspar 
  or 
  other 
  crystals 
  as 
  having 
  been 
  formed 
  while 
  the 
  rock 
  

   was 
  still 
  in 
  a 
  molten 
  state. 
  

  

  In 
  a 
  very 
  valuable 
  and 
  suggestive 
  memoir, 
  to 
  which 
  I 
  shall 
  more 
  

   particularly 
  refer 
  in 
  the 
  sequel, 
  Dr. 
  Erasmus 
  Haworth, 
  after 
  describ- 
  

   ing 
  some 
  very 
  remarkable 
  examples 
  of 
  these 
  outgrowths 
  in 
  the 
  

   felspars 
  of 
  granitic 
  rocks 
  from 
  Missouri, 
  and 
  discussing 
  all 
  the 
  

   possible 
  explanations 
  of 
  them, 
  decided 
  in 
  favour 
  of 
  their 
  having 
  

   been 
  produced 
  before 
  the 
  complete 
  consolidation 
  of 
  the 
  mass 
  in 
  which 
  

   the 
  crystals 
  occur 
  ***. 
  

  

  The 
  first 
  petrographer 
  who 
  seems 
  to 
  have 
  suspected 
  that 
  such 
  

   outgrowths 
  might 
  have 
  occurred 
  after 
  the 
  consolidation 
  of 
  the 
  rock 
  

   was 
  Dr. 
  E. 
  Becke 
  ; 
  and 
  this 
  view 
  is 
  indicated 
  in 
  his 
  very 
  remarkable 
  

   and 
  thoughtful 
  memoir 
  on 
  the 
  " 
  Eruptivgesteine 
  aus 
  der 
  Gneiss- 
  

   formation 
  des 
  niederosterreichische 
  Waldviertels 
  " 
  tft- 
  He 
  appears 
  

   to 
  have 
  seen 
  that 
  certain 
  secondary 
  growths 
  in 
  hornblende 
  -crystals 
  

   must 
  have 
  gone 
  on 
  when 
  the 
  rock 
  was 
  in 
  a 
  solid 
  state. 
  In 
  1887 
  

   Mr. 
  Van 
  Hise 
  announced 
  that 
  he 
  had 
  found 
  similar 
  secondary 
  out- 
  

  

  * 
  Quart. 
  Journ. 
  Geol. 
  Soc. 
  vol. 
  xxxv. 
  (1879), 
  p. 
  666, 
  and 
  subsequent 
  memoirs, 
  

   t 
  Ibid. 
  vol. 
  xxxvii. 
  1881, 
  p. 
  6. 
  

  

  \ 
  Am. 
  Journ. 
  Sci. 
  3rd 
  ser. 
  vol. 
  xxvii. 
  (1884), 
  p. 
  399. 
  

   § 
  Am. 
  Journ. 
  Sci. 
  3rd 
  ser. 
  vol. 
  xxx. 
  (1885), 
  p. 
  231. 
  

   || 
  Quart. 
  Journ. 
  Geol. 
  Soc. 
  vol. 
  xliv. 
  (1888), 
  p. 
  15. 
  

   f 
  Neues 
  Jahrb. 
  fur 
  Min. 
  &c. 
  1881, 
  Bandii. 
  p. 
  180. 
  

   ** 
  Ibid. 
  Beilage-Band 
  ii. 
  pp. 
  605-607. 
  

   ft 
  Min. 
  und 
  petr. 
  Mitth. 
  vol. 
  v. 
  p. 
  147, 
  &o. 
  

   It 
  Zeitschr. 
  d. 
  d. 
  geol. 
  Ges. 
  vol. 
  xxxv. 
  1883, 
  p. 
  489. 
  

   §§ 
  Sitzungsb. 
  der 
  k. 
  k. 
  Akad. 
  Wiss. 
  Wien 
  (1883), 
  i. 
  Abth. 
  

   IIP 
  Neues 
  Jahrb. 
  fur 
  Min. 
  &e. 
  (1834), 
  Band 
  i. 
  pp. 
  18-44. 
  

   %% 
  Jahrb. 
  der. 
  k. 
  preuss. 
  geol. 
  Landesanstalt 
  (1887), 
  pp. 
  77-78 
  & 
  98. 
  

   *** 
  The 
  Archaean 
  Geology 
  of 
  Missouri 
  (Minneapolis, 
  Minn. 
  1888), 
  pp. 
  16-17. 
  

   This 
  paper 
  also 
  appeared 
  in 
  the 
  American 
  Geologist 
  for 
  May 
  and 
  June 
  1888. 
  

   ttt 
  Min. 
  und 
  petr. 
  Mitth. 
  vol. 
  v. 
  (1883), 
  pp. 
  158, 
  159, 
  171, 
  &c. 
  

  

  p 
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