626  Vegetation  of  Yellowstone  Hot  Springs.  {^^"ber^iS?1, 
with  a  hairy  or  woolly  covering  are  thus  secure  against  frost  action. 
The  plants  of  the  Yellowstone  region,  as  far  as  observed,  are  well 
adapted  to  their  surroundings. 
The  forests  are  formed  by  one  tree  predominating,  Pinus  contorta, 
var.  Murrayana,  which  grows  tall  and  straight,  but  never  reaches 
any  considerable  girth.  Interspersed  among  the  pines  we  find  sev- 
eral other  arborescent  species,  namely,  Douglass  spruce,  Pseudotsuga 
Douglasii,  the  largest  tree  in  the  park;  balsam,  Abies  subalpina,  pine, 
Pinus  Engelmannii,  red  cedar,  Juniperus  Virginiana,  poplar,  Popu- 
lus  tremuloides,  and  willow,  Salix,  of  several  species.  These  forests 
are  of  great  importance  in  conserving  the  rain  which  falls.  Many 
of  the  most  important  rivers  of  the  western  United  States  rise  in 
this  region,  the  Missouri,  the  Yellowstone,  the  Wind,  the  Big  Horn, 
the  Platte,  the  Green  (afterward  the  Colorado),  and  the  Snake, 
which  flows  through  Wyoming,  Idaho  and  Washington,  emptying 
into  the  Columbia,  and  thus  reaches  the  Pacific. 
Yellowstone  Park,  notwithstanding  its  wild  grandeur  as  a  moun- 
tain domain,  is  yet  more  interesting  on  account  of  the  geological 
wonders  which  are  found  within  its  boundaries,  namely  the  geysers 
and  hot  springs.  The  geysers  are  actively  throwing  up  in  jets  at 
periodic  intervals,  steam  and  boiling  water ;  the  hot  springs  are 
either  quiescent,  or  are  bubbling  and  boiling  without  explosive  erup- 
tion. They  are  found  in  four  distinct  areas  in  the  Park;  the  geysers 
and  the  hot  springs  in  the  Upper,  Lower  and  Norris  Geyser  Basin, 
hot  springs  only  in  the  Mammoth  Hot  Spring  Region.  This  divis- 
ion also  accords  with  the  predominating  chemical  content  of  the 
waters.  In  the  Upper,  Lower  and  Norris  Geyser  Basins,  we  have 
springs  and  geysers  which  are  actively  depositing  silicious  material 
(sinter);  in  the  Mammoth  Hot  Spring  Basin,  springs  which  are 
forming  calcareous  deposits,  called  travertine. 
Much  inquiry  has  been  instituted  concerning  the  therapeutic  value 
of  the  mineral  springs  of  the  Park.  Many  hot  spring  regions  through- 
out Europe  and  America  are  resorted  to  by  thousands  in  search  of 
health.  The  hot  springs  of  Virginia  are  visited  by  hundreds  every 
year.  It  is  said  of  the  Yellowstone  region,  that  the  first  explorers 
to  ascend  the  Gardiner  River,  in  187 1,  found  numbers  of  invalids 
encamped  on  the  banks,  where  the  hot  waters  from  Mammoth  Hot 
Springs  enter  the  stream ;  and  it  is  recorded  that  they  were  most 
emphatic  in  their  favorable  impressions  in  regard  to  their  sanitary 
