﻿106 
  Thietieth 
  Repokt 
  on 
  the 
  State 
  Museum. 
  

  

  they 
  had 
  undergone 
  incipient 
  alteration, 
  but 
  for 
  the 
  most 
  part 
  

   do 
  not 
  alter 
  in 
  tint 
  with 
  crossed 
  Mchols. 
  They 
  were 
  referred 
  

   to 
  diallage. 
  

  

  In 
  reference 
  to 
  the 
  nature 
  of 
  this 
  pyroxene, 
  the 
  following 
  

   remarks 
  by 
  Zirkel 
  * 
  are 
  of 
  interest 
  : 
  

  

  The 
  diallage 
  is 
  usually 
  filled 
  with 
  a 
  multitude 
  of 
  foreign 
  

   microscopic 
  lamellae 
  and 
  needle-like 
  microliths, 
  and 
  exhibits 
  

   often 
  a 
  highly 
  fibrous 
  appearance. 
  This 
  occurs 
  upon 
  the 
  prin- 
  

   cipal 
  cleavage 
  plane, 
  the 
  orthopinakoid, 
  and 
  distinguishes 
  it 
  

   from 
  most 
  augites. 
  By 
  its 
  very 
  feeble 
  dichroism, 
  on 
  which 
  

   account 
  no 
  manifest 
  difference 
  of 
  tint 
  is 
  obtained 
  on 
  trial 
  with 
  

   a 
  Nichol's 
  prism, 
  it 
  is 
  connected 
  however 
  with 
  augite, 
  just 
  as 
  

   through 
  the 
  same 
  property 
  it 
  is 
  distinguished 
  from 
  hypersthene 
  

   and 
  hornblende. 
  Apart 
  from 
  the 
  difference 
  in 
  chemical 
  com- 
  

   position 
  and 
  its 
  other 
  optical 
  properties, 
  on 
  account 
  of 
  this 
  

   absence 
  of 
  dichroism, 
  must 
  those 
  constituents 
  of 
  the 
  "Hyper- 
  

   sthenites" 
  of 
  Veltlin, 
  of 
  Penig 
  and 
  Neurode, 
  and 
  of 
  the 
  isle 
  of 
  

   Skye, 
  which 
  were 
  formerly 
  supposed 
  to 
  be 
  hypersthene, 
  be 
  

   now 
  regarded 
  as 
  diallage. 
  

  

  The 
  diallages 
  in 
  the 
  norites 
  of 
  the 
  Hebrides 
  are 
  in 
  the 
  rock- 
  

   sections 
  greyish-green 
  and 
  brownish-yellow. 
  They 
  usually 
  

   abound 
  in 
  small 
  needles, 
  which 
  are 
  arranged 
  in 
  the 
  section 
  in 
  

   a 
  parallel 
  manner, 
  but 
  present 
  among 
  themselves 
  two 
  parallel- 
  

   systems 
  cutting 
  one 
  another 
  obliquely. 
  These 
  needles 
  appear 
  

   to 
  be 
  identical 
  with 
  those 
  observed 
  in 
  the 
  neighboring 
  plagio- 
  

   clase 
  of 
  the 
  norite. 
  They 
  are 
  sometimes 
  dark, 
  sometimes 
  feebly 
  

   translucent, 
  regular 
  and 
  irregular, 
  of 
  larger 
  or 
  smaller 
  size, 
  

   disseminated 
  in 
  clusters 
  or 
  in 
  single 
  grains. 
  The 
  Norwegian 
  

   norites, 
  according 
  to 
  B,. 
  Hagge,f 
  from 
  Krageroe, 
  is 
  filled 
  even 
  

   to 
  the 
  point 
  of 
  opacity 
  with 
  dark 
  brown 
  or 
  black 
  lamellae, 
  

   which 
  lie 
  in 
  two 
  directions 
  at 
  right 
  angles 
  to 
  one 
  another. 
  In 
  

   the 
  Scottish 
  norites 
  from 
  Mull 
  and 
  Skye 
  the 
  gradual 
  conver- 
  

   sion 
  of 
  the 
  compact 
  scarcely 
  dichroic 
  diallage 
  into 
  the 
  delicate 
  

   aggregates 
  of 
  yellowish-green 
  brush-like 
  masses 
  of 
  hornblende, 
  

   which 
  are 
  at 
  the 
  same 
  time 
  strongly 
  dichroic, 
  can 
  be 
  most 
  

   distinctly 
  followed. 
  

  

  21. 
  Section 
  of 
  the 
  Dolerite, 
  whose 
  analysis 
  has 
  previously 
  

  

  *F. 
  Zirkel, 
  ib. 
  p. 
  181. 
  v 
  

  

  fMikr. 
  Untersuckungen 
  uber 
  Gabbro 
  und 
  verwandte 
  Gesteine. 
  Kiel 
  1871 
  

   Quoted 
  by 
  Zirkel, 
  loc. 
  cit. 
  p. 
  182. 
  

  

  