﻿390 
  Scientific 
  Intelligence. 
  

  

  2. 
  An 
  Estimate 
  of 
  the 
  Geological 
  Age 
  of 
  the 
  Earth 
  ; 
  by 
  J 
  

   JoLY, 
  University 
  of 
  Dublin. 
  — 
  The 
  latest 
  contribution 
  to 
  the 
  sub- 
  

   ject 
  ably 
  argued 
  by 
  Sir 
  Archibald 
  Geikie 
  at 
  the 
  meeting 
  of 
  the 
  

   J^ritish 
  Association 
  (see 
  above), 
  is 
  that 
  by 
  Professor 
  J. 
  Joly 
  in 
  a 
  

   paper 
  published 
  in 
  vol. 
  vii 
  of 
  the 
  Scientific 
  Transactions 
  of 
  the 
  

   Royal 
  Dublin 
  Society, 
  September, 
  1899. 
  In 
  this 
  interesting 
  

   memoir 
  the 
  author 
  discusses 
  the 
  geological 
  age 
  of 
  the 
  earth 
  since 
  

   the 
  formation 
  of 
  the 
  ocean, 
  basing 
  his 
  calculations 
  upon 
  the 
  time 
  

   required 
  to 
  supply 
  to 
  it 
  the 
  amount 
  of 
  sodium 
  now 
  present 
  in 
  the 
  

   water. 
  He 
  starts 
  with 
  the 
  assumption 
  of 
  the 
  Uniformitarian, 
  that 
  

   the 
  processes 
  now 
  going 
  on 
  may 
  be 
  considered 
  to 
  have 
  continued 
  

   essentially 
  as 
  at 
  present 
  for 
  the 
  whole 
  period 
  in 
  the 
  past 
  here 
  con- 
  

   cerned. 
  The 
  basis 
  on 
  which 
  his 
  argument 
  is 
  placed 
  will 
  be 
  under- 
  

   stood 
  from 
  the 
  following 
  paragraphs. 
  

  

  "In 
  the 
  method 
  of 
  approaching 
  the 
  question 
  of 
  the 
  Age 
  of 
  the 
  

   Earth 
  advanced 
  in 
  this 
  paper, 
  the 
  foregoing 
  tenet* 
  requires 
  only 
  

   acceptation 
  in 
  part 
  — 
  that 
  part 
  of 
  it 
  which 
  refers 
  to 
  the 
  removal 
  

   of 
  the 
  land 
  surface 
  by 
  solution. 
  It 
  has 
  to 
  be 
  accepted 
  as 
  a 
  

   preliminary 
  step 
  that 
  this, 
  on 
  the 
  whole, 
  has 
  been 
  constant. 
  

   Herein 
  are 
  involved 
  a 
  constancy, 
  within 
  certain 
  fairly 
  wide 
  limits, 
  

   of 
  rainfall 
  over 
  the 
  land 
  areas 
  ; 
  a 
  constancy 
  within 
  fairly 
  wide 
  

   limits 
  (which 
  can 
  roughly 
  be 
  defined) 
  of 
  the 
  exposed 
  land 
  area, 
  

   and 
  a 
  constancy 
  in 
  the 
  nature 
  and 
  rate 
  of 
  solvent 
  actions 
  going 
  

   on 
  over 
  the 
  land 
  surfaces. 
  The 
  grounds 
  on 
  which 
  this 
  amount 
  of 
  

   uniformity 
  is 
  accepted 
  are 
  given 
  in 
  this 
  paper. 
  One 
  other 
  tenet 
  

   must 
  be 
  accepted, 
  that 
  the 
  primeval 
  ocean 
  — 
  that 
  formed 
  on 
  first 
  

   condensation 
  of 
  the 
  water 
  upon 
  the 
  land 
  — 
  did 
  not 
  contain 
  the 
  

   amount 
  of 
  dissolved 
  sodium 
  now 
  entering 
  so 
  largely 
  into 
  its 
  con- 
  

   stitution. 
  The 
  grounds 
  upon 
  which 
  this 
  is 
  claimed 
  are 
  also 
  dealt 
  

   with 
  further 
  on. 
  

  

  " 
  How 
  can 
  these 
  data 
  be 
  used 
  to 
  determine 
  what 
  may 
  be 
  termed 
  

   the 
  Epigene 
  Age 
  of 
  the 
  Earth 
  ? 
  In 
  the 
  sea 
  or 
  in 
  its 
  deposits 
  

   those 
  elements 
  are 
  recognizable 
  which 
  enter 
  also 
  into 
  the 
  con- 
  

   stituents 
  of 
  the 
  solid 
  part 
  of 
  the 
  Earth's 
  crust. 
  In 
  the 
  rivers 
  

   these 
  elements 
  are 
  also 
  recognizable 
  as 
  being 
  continually 
  poured 
  

   into 
  the 
  ocean. 
  Very 
  accurate 
  estimates 
  of 
  the 
  quantities 
  of 
  

   these 
  elements 
  in 
  the 
  ocean 
  exist. 
  The 
  dissolved 
  contents 
  of 
  

   many 
  of 
  the 
  great 
  rivers 
  of 
  the 
  Earth 
  and 
  the 
  mean 
  composition 
  

   and 
  mean 
  volume 
  of 
  the 
  entire 
  river 
  discharge 
  have 
  been 
  

   estimated. 
  

  

  "Now 
  if 
  any 
  of 
  the 
  elements 
  entering 
  the 
  ocean 
  is 
  not 
  again 
  

   withdrawn, 
  but 
  is, 
  in 
  a 
  word, 
  ' 
  trapped 
  ' 
  therein, 
  re-appears 
  as 
  no 
  

   extensive 
  marine 
  deposit, 
  and 
  is 
  not 
  laid 
  down 
  sensibly 
  upon 
  its 
  

   floor; 
  and 
  if 
  the 
  amount 
  of 
  Uniformity 
  already 
  defined 
  is 
  

   accepted, 
  evidently 
  in 
  the 
  rate 
  of 
  annual 
  accretion 
  by 
  the 
  ocean 
  

   from 
  the 
  rivers 
  of 
  this 
  substance 
  and 
  the 
  amount 
  of 
  it 
  now 
  in 
  

   the 
  ocean, 
  the 
  whole 
  period 
  since 
  the 
  beginning 
  of 
  its 
  supply 
  can 
  

   be 
  estimated. 
  

  

  *[That 
  the 
  rate 
  of 
  removal 
  of 
  the 
  suba^-ial 
  laud 
  surface 
  — 
  by 
  solution 
  and 
  

   transportatiou 
  — 
  has 
  been 
  ou 
  iho 
  whole 
  uniform 
  J 
  

  

  