﻿Washington 
  — 
  Analyses 
  of 
  Italian 
  Volcanic 
  Rocks. 
  293 
  

  

  The 
  main 
  vulcanological 
  fact 
  on 
  which 
  this 
  conclusion 
  rests 
  

   is 
  the 
  similarity 
  between 
  the 
  two 
  lines 
  in 
  the 
  order 
  and 
  direc- 
  

   tion 
  of 
  extinction 
  along 
  them. 
  Space 
  is 
  lacking 
  for 
  detailed 
  

   statement, 
  but 
  in 
  both 
  we 
  lind 
  the 
  volcanic 
  activity 
  dying 
  away 
  

   from 
  north 
  to 
  south. 
  Thus 
  the 
  volcanoes 
  of 
  Bolsena 
  and 
  

   Yiterbo 
  are 
  older 
  than 
  those 
  of 
  the 
  Alban 
  Hills, 
  where 
  erup- 
  

   tions 
  took 
  place 
  not 
  much 
  anterior 
  to 
  the 
  earliest 
  Roman 
  times, 
  

   and 
  perhaps 
  also 
  during 
  the 
  Roman 
  Republic. 
  At 
  the 
  Ernici 
  

   and 
  Rocca 
  Monfina 
  the 
  evidence 
  is 
  uncertain, 
  but 
  at 
  the 
  

   southern 
  extremity 
  there 
  is 
  the 
  still 
  active 
  volcano 
  of 
  Yesuvius. 
  

  

  Similarly 
  along 
  the 
  western 
  line 
  we 
  iind 
  to 
  the 
  north 
  the 
  

   much 
  denuded 
  remains 
  of 
  old 
  volcanoes 
  at 
  Capraia, 
  Elba 
  and 
  

   Giglio. 
  At 
  the 
  Ponza 
  Islands 
  the 
  original 
  forms 
  are 
  better 
  

   preserved, 
  though 
  extensively 
  denuded. 
  At 
  the 
  Ischian 
  region 
  

   the 
  forms 
  are 
  more 
  perfect 
  and 
  activity 
  is 
  almost 
  ended, 
  as 
  

   shown 
  by 
  the 
  eruptions 
  of 
  the 
  Solfatara, 
  Monte 
  ISTuovo 
  and 
  

   Arso, 
  and 
  other 
  facts. 
  At 
  the 
  Li 
  pari 
  Islands 
  we 
  find 
  also 
  the 
  

   remains 
  of 
  large 
  volcanoes, 
  and 
  activity 
  is 
  still 
  kept 
  up 
  to 
  a 
  

   certain 
  extent 
  at 
  the 
  small 
  vents 
  of 
  Yulcano 
  and 
  Stromboli.* 
  

   At 
  Etna 
  alone, 
  near 
  the 
  extreme 
  south 
  end 
  of 
  the 
  line, 
  do 
  we 
  

   find 
  a 
  typical 
  volcano, 
  in 
  a 
  comparatively 
  perfect 
  state 
  and 
  in 
  

   full 
  activity, 
  — 
  comparable 
  with 
  Yesuvius. 
  

  

  It 
  may 
  also 
  be 
  noted 
  that 
  there 
  seems 
  to 
  be 
  a 
  tendency 
  for 
  

   the 
  later 
  lavas 
  to 
  be 
  more 
  basic 
  than 
  the 
  earlier, 
  as 
  has 
  been 
  

   pointed 
  out 
  in 
  general 
  for 
  the 
  Bolsena- 
  Yesuvius 
  line,t 
  and 
  as 
  

   may 
  be 
  exemplified 
  by 
  the 
  rocks 
  of 
  the 
  Alban 
  Hills, 
  Yesuvius, 
  

   Stromboli:}: 
  and 
  Etna. 
  

  

  That 
  the 
  petrographical 
  provinces 
  of 
  the 
  Bolsena- 
  Yesuvius 
  

   line 
  and 
  of 
  the 
  groups 
  of 
  Ponza, 
  Ischia, 
  the 
  Lipari 
  Islands 
  and 
  

   Etna 
  are 
  quite 
  distinct 
  is 
  well 
  known, 
  § 
  but 
  it 
  is 
  less 
  generally 
  

   supposed 
  or 
  accepted 
  that 
  a 
  well 
  marked 
  line 
  exists 
  — 
  now 
  

   largely 
  covered 
  by 
  the 
  waters 
  of 
  the 
  Mediterranean 
  — 
  which 
  is 
  

   parallel 
  to 
  the 
  other 
  and 
  quite 
  distinct 
  from 
  it, 
  and 
  that 
  the 
  

   rocks 
  of 
  Ischia 
  and 
  the 
  Phlegraean 
  Fields 
  are 
  not 
  genetically 
  

   connected 
  with 
  those 
  of 
  the 
  neighboring 
  Yesuvian 
  vent. 
  

  

  In 
  this 
  connection 
  it 
  may 
  be 
  suggested 
  as 
  a 
  tentative 
  hypoth- 
  

   esis 
  that 
  another 
  parallel 
  fracture-line 
  is 
  to 
  be 
  found 
  to 
  the 
  

   southwest, 
  which 
  extends 
  from 
  the 
  small 
  islets 
  of 
  Linosa 
  and 
  

   Lamped 
  usa, 
  southwest 
  of 
  Malta, 
  through 
  Pantellaria 
  to 
  Sardinia. 
  

   Concerning 
  the 
  first 
  two 
  islets 
  our 
  information 
  is 
  of 
  the 
  scan- 
  

   tiest, 
  it 
  being 
  only 
  known 
  that 
  they 
  are 
  volcanic. 
  [ 
  Rosen- 
  

  

  *Cf. 
  Bonney, 
  Volcanoes, 
  1899, 
  pp. 
  198-201. 
  

   f 
  Cf. 
  Journ. 
  Geol., 
  v, 
  p. 
  376, 
  1897. 
  

  

  X 
  Cortese 
  and 
  Sabatini, 
  op. 
  cit., 
  p. 
  84. 
  The 
  rocks 
  of 
  Yulcaoo 
  are 
  also 
  generally 
  

   basic, 
  but 
  those 
  of 
  the 
  last 
  eruption 
  are 
  rather 
  acid. 
  (Op. 
  cit 
  , 
  p. 
  114.) 
  

   § 
  Cf. 
  Bonney, 
  Yolcanoes, 
  p. 
  197. 
  

   II 
  Scrope, 
  Volcanoes, 
  1862, 
  p. 
  345. 
  

  

  