30  THE  GOLDEN  PARALLELS. 
that  at  the  "beach  diggings"  in  California,  a  blush  sand,  not  un- 
like the  pipe  clay  of  Ballarat,  is  frequently  thrown  up  by  the 
waves,  and  is  found  to  contain  gold  in  considerable  quantities. 
The  conclusion  arrived  at  by  this  reasoning  is  that  the  great 
gold  fields  of  the  world,  as  at  present  known,  are  included  in  the 
vast  system  of  volcanic  rocks  which  surround  the  Pacific.  This 
chain,  though  broken  here  and  there,  is  said  to  be  traceable  be- 
tween Australia  and  America,  and  to  be  easy  of  identification  on 
both  sides  of  the  ocean.  Such  a  continuous  and  well-marked 
line  of  volcanic  elevation  has  often  received  the  attention  of  ge- 
ologists. Humboldt's  view,  which  is  the  one  generally  accepted 
on  the  subject,  is  that  the  bed  of  the  Pacific  attained  its  present 
depth  at  a  comparatively  late  period;  that  its  unbroken  crust, 
pressed  down  on  the  molten  mass  underneath,  caused  a  quantity 
of  it  to  rush  towards  the  line  of  fracture  at  the  edges,  and  that 
this  disturbed  matter  found  vent  in  the  elevations  which  are  now 
connected  with  the  gold  fields  of  America  and  Australia.  So 
far  these  considerations,  as  bearing  on  the  science  of  geology, 
are  highly  important ;  but  it  has  to  be  shown  in  what  way  gold 
is  to  be  connected  with  volcanic  shocks  in  some  places  and  not 
in  others.  On  this  point  it  is  to  be  laid  down  by  Sir  Roderick 
Murchison  that  the  rocks  which  are  the  most  auriferous  are  of 
the  Silurian  age,  and  that  a  certain  geological  zone  only  in  the 
crust  of  the  globe  is  auriferous  at  all.  Gold,  he  states,  has 
never  been  found  in  any  stratified  formations  composed  of  sec- 
ondary or  tertiary  deposits,  but  only  in  crystalline  and  palaeozoic 
rocks,  or  in  the  drift  from  those  rocks.  The  most  usual  original 
position  of  the  metal  is  in  quartzose  veinstones  that  traverse  al- 
tered Silurian  slates,  frequently  near  their  junction  with  erup- 
tive rocks.  Sometimes,  however,  it  is  partially  diffused  through 
the  body  of  rocks  of  igneous  origin.  From  this  it  appears  that 
volcanic  eruptions,  in  connection  with  Silurian  rocks,  are  to  be 
regarded  as  the  origin  of  gold  formations. 
It  will  have  been  seen  that,  according  to  the  volcanic  basin 
theory  as  described  above,  the  auriferous  rocks  which  surround 
the  Pacific  leave  Victoria  and  plunge  into  the  sea  to  appear 
again  on  the  other  side  of  Bass'  Straits.  This  would,  of  course, 
leave  South  Australia  out  of  the  reach  of  these  gold-bearing 
