630  Vegetation  of  Yellowstone  Hot  Springs.     {^im^itar  ' 
pose.  The  description  of  Dr.  Peale  is  interestingly  comprehensive, 
and  is  as  follows :  "  This  is  one  of  the  most  beautiful  springs  in  the 
Upper  Basin.  It  has  a  delicate  rim,  with  toadstool-like  masses 
around  it.  The  basin  slopes  rather  gently  toward  a  central  aperture, 
that,  to  the  eye,  appears  to  have  no  bottom.  The  water  in  the 
spring  has  a  delicate  turquoise  tint,  and  as  the  breeze  sweeps  across 
its  surface,  dispelling  the  steam,  the  effect  of  the  ripple  of  the  water 
is  very  beautiful.  The  sloping  sides  are  covered  with  a  light  brown 
crust ;  sometimes  it  is  rather  a  cream  color.  The  funnel  is  about 
40  feet  in  diameter,  while  the  entire  space  covered  by  the  spring 
is  about  55  x  60  feet,  outside  the  rim  of  which  is  a  border  of  pitch 
stone  (obsidian)  sand  or  gravel,  sloping  25  feet.  From  its  west 
side  flows  a  considerable  stream,  forming  a  most  beautiful  chan- 
nel, in  which  the  coloring  presents  a  remarkable  variety  of  shades ; 
the  extremely  delicate  pinks  are  mingled  with  equally  delicate  tints 
of  saffron  and  yellow,  and  here  and  there  shades  of  green." 
The  overflow  from  this  spring  spreads  out  over  a  large  area,  called 
Specimen  Lake,  where  absorption  of  the  silica  from  the  water  has 
destroyed  many  of  the  trees  of  the  vicinity,  the  dry,  lifeless  trunks 
adding  to  the  attractiveness  of  the  place  by  affording  the  appear- 
ance of  petrifactions.1  All  of  these  exquisite  masses  of  colors  which 
are  found  lining  the  pools,  filling  the  overflow  channels  and  spread- 
ing out  flat  in  the  lower  marshy  places,  are  due  to  the  growth  of 
vegetal  organisms  belonging  to  the  bacteria  and  algae. 
Walter  H.  Weed2  describes  the  appearance  of  the  Black  Sand 
Basin  and  channels  filled  with  algal  growths :  "  As  the  water  from 
this  spring  flows  along  its  channel  it  is  rapidly  chilled  by  contact 
with  the  air  and  by  evaporation,  and  is  soon  cool  enough  to  permit 
the  growth  of  the  more  rudimentary  forms  which  live  at  the  highest 
temperature.  These  appear  first  in  skeins  of  delicate  white  filaments 
which  gradually  change  to  pale  flesh-pink  farther  down  stream.  As 
the  water  becomes  cooler,  this  pink  becomes  deeper,  and  a  bright 
orange  and  closely  adherent  fuzzy  growth,  rarely  filamentous, 
appears  at  the  border  of  the  stream,  and  finally  replaces  the  first- 
mentioned  forms.  This  merges  into  yellowish-green,  which  shades 
into  a  rich  emerald  farther  down,  this  being  the  common  color  of 
fresh-water  algae.  In  the  quiet  waters  of  the  pools  fed  by  this  stream 
1  Haynes-Guptill,  Guide  to  Yellowstone  Park,  p.  68. 
3  Weed,  Ninth  Annual  Report  U.  S.  Geological  Survey,  p.  657. 
