﻿For 
  some 
  years 
  I 
  have 
  been 
  occupied 
  witli 
  an 
  examination 
  

   of 
  the 
  Diatoms 
  which 
  are 
  found 
  imbedded 
  in 
  the 
  quarternary 
  

   layers 
  of 
  Sweden, 
  for 
  the 
  purpose 
  of 
  determining 
  the 
  circum- 
  

   stances 
  under 
  which 
  these 
  layers 
  have 
  been 
  deposited. 
  Du- 
  

   ring 
  this 
  research 
  I 
  found 
  that 
  a 
  great 
  part 
  of 
  the 
  younger 
  

   deposits 
  of 
  eastern 
  Sweden, 
  viz: 
  black-clay 
  (svartlera), 
  post- 
  

   glacialclay 
  (åkerlera), 
  alluvialclay 
  and 
  sand, 
  silt 
  (gyttja), 
  

   siltyclay 
  (gyttjeler), 
  peat 
  and 
  shellbeds 
  contained 
  valves 
  of 
  

   naarine 
  Diatoms, 
  and 
  this, 
  in 
  connection 
  with 
  the 
  proximity 
  

   to 
  the 
  Baltic 
  of 
  the 
  region 
  where 
  these 
  layers 
  were 
  taken, 
  

   indicated 
  this 
  sea 
  as 
  the 
  place 
  where 
  they 
  were 
  formed. 
  

  

  It 
  was 
  of 
  course 
  of 
  considerable 
  interest 
  to 
  know, 
  whether 
  

   the 
  diatoms, 
  imbedded 
  in 
  these 
  layers, 
  were 
  the 
  same 
  species 
  

   as 
  those 
  that 
  still 
  form 
  the 
  diatomaceous 
  flora 
  of 
  the 
  Baltic, 
  

   or 
  if 
  some 
  alteration 
  of 
  species 
  had 
  taken 
  place, 
  and 
  in 
  that 
  

   case, 
  if 
  the 
  change 
  showed 
  a 
  decrease 
  of 
  the 
  saltness 
  of 
  

   the 
  water. 
  

  

  But 
  in 
  the 
  literature 
  on 
  Diatoms, 
  which 
  was 
  known 
  to 
  

   rae, 
  the 
  notices 
  about 
  the 
  Baltic 
  species 
  were 
  very 
  scarce, 
  

   and 
  the 
  number 
  of 
  the 
  forms, 
  enumerated 
  as 
  occurring 
  in 
  

   the 
  Baltic 
  Sea, 
  rather 
  small. 
  J. 
  Schumann 
  ^), 
  in 
  his 
  first 
  

   paper 
  on 
  Prussian 
  Diatoms, 
  mentions 
  only 
  23 
  species 
  as 
  li- 
  

   ving 
  in 
  the 
  Baltic, 
  Cleve 
  in 
  »Svenska 
  och 
  Norska 
  Diatoma- 
  

   céer», 
  has 
  24 
  Baltic 
  species, 
  and 
  a 
  list 
  of 
  the 
  species 
  occur- 
  

   ring 
  in 
  the 
  harbour 
  of 
  Travemunde 
  ^) 
  contains 
  37 
  forms. 
  

   So 
  ScHUMANN 
  ^), 
  in 
  his 
  second 
  paper, 
  says 
  that 
  the 
  Baltic 
  is 
  

   very 
  poor 
  in 
  diatoms, 
  a 
  fact 
  that 
  is 
  caused 
  by 
  the 
  low 
  salt- 
  

   ness 
  of 
  its 
  water. 
  But 
  on 
  the 
  contrary 
  it 
  seems 
  as 
  a 
  sea 
  

   which, 
  like 
  the 
  Baltic, 
  opens 
  into 
  the 
  ocean, 
  and 
  into 
  which, 
  

   on 
  the 
  other 
  hand, 
  a 
  great 
  number 
  of 
  rivers 
  pour 
  their 
  fresh 
  

  

  ') 
  ScHUM. 
  1862. 
  

  

  2) 
  Ostsee 
  Exp. 
  1871. 
  

  

  3) 
  SCHUM. 
  1864. 
  

  

  