﻿292 
  Washingto7i 
  — 
  Analyses 
  of 
  Italian 
  Volcanic 
  Bochs. 
  

  

  di 
  Noto 
  in 
  Sicily.^ 
  It 
  is 
  impossible 
  here 
  to 
  go 
  into 
  a 
  descrip- 
  

   tion 
  of 
  all 
  these, 
  for 
  which 
  the 
  reader 
  ma}^ 
  turn 
  to 
  the 
  refer- 
  

   ences 
  given. 
  It 
  must 
  suffice 
  to 
  state 
  that 
  at 
  Capraia 
  we 
  find 
  

   andesites, 
  at 
  the 
  Ponza 
  and 
  Liparif 
  Islands 
  rhjolites, 
  trachytes, 
  

   latites 
  and 
  a 
  few 
  basalts, 
  while 
  at 
  Etna:}: 
  and 
  Yal 
  di 
  Noto 
  there 
  

   have 
  been 
  erupted 
  only 
  normal 
  basalts 
  of 
  a 
  fairly 
  uniform 
  com- 
  

   position. 
  From 
  the 
  analyses 
  of 
  the 
  rocks 
  of 
  these 
  localities 
  it 
  

   is 
  evident 
  that 
  they 
  differ 
  also 
  chemically 
  from 
  those 
  of 
  the 
  

   Bolsena-Yesuvius 
  line, 
  Na^O 
  being 
  higher 
  than 
  K^O 
  (except 
  in 
  

   the 
  rhyolites), 
  though 
  here 
  also 
  CaO 
  is 
  apt 
  to 
  be 
  rather 
  high. 
  

  

  Consideration 
  of 
  these 
  facts 
  leads 
  to 
  the 
  conclusion 
  that 
  the 
  

   rocks 
  of 
  Ischia 
  and 
  the 
  Phlegrsean 
  Fields 
  are 
  related 
  rather 
  

   to 
  those 
  of 
  the 
  other 
  islands 
  than 
  to 
  those 
  of 
  the 
  main 
  Bolsena- 
  

   Yesuvius 
  line, 
  and, 
  while 
  the 
  data 
  at 
  hand 
  are 
  perhaps 
  insuffi- 
  

   cient, 
  I 
  would 
  express 
  the 
  view 
  that 
  they 
  are 
  not 
  genetically 
  

   connected 
  (at 
  least 
  in 
  an 
  immediate 
  way) 
  with 
  the 
  closely 
  adja- 
  

   cent 
  rocks 
  of 
  Somma 
  and 
  Yesuvius. 
  

  

  The 
  idea 
  that 
  a 
  volcanic 
  fracture-line 
  exists 
  west 
  of 
  the 
  

   Italian 
  peninsula 
  was 
  first 
  broached 
  by 
  Pilla 
  in 
  181:2, 
  supported 
  

   by 
  Doelter 
  and 
  Suess, 
  expressed 
  in 
  a 
  somewhat 
  modified 
  form 
  

   by 
  Ponzi, 
  and 
  has 
  lately 
  been 
  taken 
  up 
  by 
  Ricciardi.§ 
  This 
  last 
  

   writer 
  bases 
  his 
  conclusions 
  partly 
  on 
  stratigraphical 
  observa- 
  

   tions, 
  but 
  largely 
  in 
  a 
  chemical 
  way 
  on 
  the 
  amount 
  of 
  SiO„ 
  in 
  

   the 
  various 
  rocks. 
  

  

  That 
  the 
  amount 
  of 
  SiOj 
  alone 
  is 
  not 
  a 
  proper 
  nor 
  sufficient 
  

   basis 
  on 
  which 
  to 
  compare 
  rocks 
  of 
  various 
  regions 
  is 
  a 
  fact 
  

   that 
  will 
  scarcely 
  be 
  disputed 
  by 
  any 
  petrographer. 
  But 
  from 
  

   a 
  broader 
  point 
  of 
  view, 
  embracing 
  all 
  the 
  chemical 
  and 
  miner- 
  

   alogical 
  characters 
  of 
  the 
  various 
  rocks, 
  as 
  well 
  as 
  from 
  other, 
  

   topographical, 
  vulcanological 
  and 
  stratigraphical 
  considerations, 
  

   it 
  would 
  seem 
  that 
  the 
  conclusion 
  is 
  justified 
  that 
  a 
  volcanic 
  

   fracture-line 
  exists 
  west 
  of 
  the 
  coast 
  of 
  Italy 
  and 
  parallel 
  with 
  

   it, 
  extending 
  from 
  Capraia, 
  through 
  the 
  Ponza 
  Islands, 
  Ischia 
  

   and 
  the 
  Phlegrsean 
  Fields, 
  the 
  Lipari 
  Islands, 
  and 
  ending 
  

   probably 
  in 
  Sicily 
  at 
  Etna 
  and 
  Yal 
  di 
  Noto. 
  

  

  * 
  Ricciardi, 
  Gazz. 
  Chim. 
  Ttal 
  , 
  xl/p. 
  ITI, 
  1881. 
  

  

  f 
  It 
  may 
  be 
  remarked 
  that 
  I 
  have 
  been 
  able 
  to 
  find 
  no 
  g-ood 
  analysis 
  of 
  the 
  well 
  

   known 
  rocks 
  of 
  these 
  islands, 
  with 
  the 
  exception 
  of 
  one 
  of 
  an 
  apparently 
  

   abnormal 
  type 
  described 
  by 
  Hobbs 
  (Bull. 
  Geol. 
  Soc. 
  Am., 
  v. 
  p 
  599, 
  1898), 
  those 
  

   of 
  Abich(Yulk. 
  Ersch., 
  1841, 
  pp. 
  25, 
  62) 
  and 
  of 
  Baltzer 
  (Zeit. 
  d. 
  dent, 
  geol 
  Ges., 
  

   xxvli, 
  p. 
  36, 
  1875) 
  bein^ 
  too 
  obviously 
  incorrect 
  to 
  merit 
  consideration— 
  a 
  striking 
  

   instance 
  of 
  the 
  imperfection 
  of 
  our 
  chemical 
  knowledge 
  of 
  igneous 
  rocks. 
  

  

  :}: 
  Johnston-Lavis 
  (Boll. 
  Soc. 
  Ital. 
  Micro. 
  Acireale, 
  i, 
  p. 
  26, 
  1888) 
  lias 
  detected 
  

   leucite 
  in 
  one 
  of 
  the 
  basalts 
  of 
  Etna 
  and 
  Backstrom 
  (Geol. 
  Foreu. 
  Forh., 
  xviii, 
  

   p. 
  ]55, 
  1896), 
  in 
  rocks 
  from 
  Volcanello. 
  

  

  § 
  Ricciardi, 
  SuU' 
  AUineamento 
  dei 
  Yulcani 
  Italiani. 
  Reggio-Kmilia, 
  1887. 
  

   References 
  to 
  the 
  other 
  authorities 
  cited 
  may 
  bo 
  found 
  in 
  this 
  paper, 
  as 
  also 
  a 
  

   map. 
  

  

  