timber1!1]™'}     Vegetation  of  Yellowstone  Hot  Springs.  633 
Gleocapsa,  a  blue-green  alga,  is  found  growing  on  the  sides  of  gey- 
ser cones,  where  steam  is  escaping,  forming  there  a  delicate  olive- 
green  coloration.  A  kind  of  fibrous  sinter  is  formed  by  the  growth 
of  the  little  alga,  Calothrix  gypsophila,  or  the  young  form  of  Mastigo- 
nema  thermale,  the  latter  olive  colored,  and  forming  the  sinter  of 
the  crater  of  the  Excelsior  Geyser.1  A  coarse  sinter  is  due  to  a 
bright  red  species,  Leptothrix,  a  finer  variety  to  Leptothrix  {Hypheo- 
thrix)  laminosa,  ranging  in  color  from  white  to  flesh  pink,  yellow 
and  red  to  green,  as  the  water  cools.  Besides  the  above  plants, 
which  belong  to  the  Bacteriace^e  and  the  Cyanophyce^c,  speak- 
ing in  a  general  way,  we  find  that  several  mosses,  Musci,  are  active 
in  the  formation  of  sinter  on  the  slopes  below  Hillside  Spring. 
These  springs  issue  from  the  rhyolite  slopes  beneath  the  cliffs  of 
the  Madison  Plateau,  and  the  waters,  whose  temperatures  are 
1840  F.-1980  F.,  contain  both  silica  and  lime  in  solution,  which 
they  deposit  in  their  downward  flow.  This  moss  has  been  deter- 
mined by  Prof.  Charles  R.  Barnes,  of  the  University  of  Wisconsin, 
to  be  Hypnum  aduncunt,  var.  grasilescens,  Br.  and  Sch. 
Besides  the  sinter  and  travertine  formed  by  algae,  which  remove 
in  the  case  of  the  carbonated  waters,  containing  calcium  bicarbonate, 
Ca  (HC03)2,  in  solution,  the  gaseous  carbon  dioxide,  thus  depositing 
calcium  carbonate,  CaC03,  we  have  stalactites  produced  by  the 
growth  of  several  algae,  Gleocapsa  violacea,  Schizothrix  calcicola, 
Synechococcus  ceruginosus  and  Phormidium  {Leptothrix)  laminosum. 
An  interesting  account  of  the  formation  of  these  stalactites  has  been 
given  to  us  by  Miss  Josephine  Tilden,  who  visited,  recently,  the 
Yellowstone  Park. 
In  the  tepid  waters  of  the  overflow  basins,  for  example  Speci- 
men Lake,  which  is  produced  by  the  water  from  the  Black  Sand 
Pool,  we  find  extensive  diatomaceous  beds  formed  by  the  growth  of 
numerous  diatoms.  The  water  of  these  areas  has  encroached  on 
the  timber,  killing  the  trees,  which  stand  as  bare  poles  from  the 
treacherous  marshes.  It  is  known  that  these  plants  deposit  silica, 
as  a  box,  test,  or  frustule,  and  it  is  thus  by  the  activity  of  the  proto- 
plasm that  the  silicious  diatomaceous  earths  are  formed.  Samples 
of  this  material  show  the  presence  of  Denticula  valida,  which  forms 
the  bulk  of  the  material,  Denticula  elegans,  Navicula  major,  N.  viri- 
dis,  Epithema,  Cocconema,  etc. 
1  Weed,  loc.  cit. 
