DESCRIPTION    OF    AUTHORITIES. 
RAILROADS. 
The  elevations  determined  by  railroad  levels  are  credited  to  the 
roads-  by  which  they  were  furnished. 
On  pages  12-19  will  be  found  a  list  of  these  railroads,  with  the 
abbreviations  used  for  their  names  arranged  alphabetically. 
Unless  otherwise  stated,  the  elevation  is  that  of  the  railroad  track 
at  the  station  of  the  road  given.  In  cases  where  two  or  more  rail- 
roads meet  or  cross  at  grade,  the  elevation  furnished  by  one  of  them 
only — the  best  determined — is  given. 
The  collection  and  adjustment  of  these  railroad  levels  has  formed 
by  far  the  greater  part  of  the  work  of  this  compilation.  There  are 
now  in  the  possession  of  this  office  abstracts  of  the  profiles  of  more 
than  nine-tenths  of  the  railroad  mileage  of  the  country,  and  all  this 
material  has  been  used  in  the  preparation  of  the  present  volume. 
For  this  material,  which  is  of  the  greatest  value  in  the  preparation  of 
topographic  maps,  as  well  as  for  other  purposes,  this  office  is  in  the 
main  indebted  directly  to  the  chief  engineers  of  the  various  railroad 
companies. 
The  interest  taken  in  this  compilation  by  railroad  engineers,  which 
was  noted  in  earlier  editions  of  this  work,  has  increased  and  spread, 
until  to-day  there  is  scarcely  a  large  railroad  corporation  which  has 
not  in  its  possession  a  full  and  consistent  profile  of  all  its  lines,  reduced 
to  a  common  datum  point,  and  these  profiles  have  been  courteously 
furnished  to  this  office.  Many  of  them  are  wonderfully  accurate, 
some  comparing  favorably  even  with  the  precise  leveling  of  the 
United  States  Coast  and  Geodetic  Survey  and  of  the  river  commis- 
sions. 
The  errors  due  to  careless  connections  between  divisions  and  sec- 
tions of  roads,  which  were  mentioned  in  former  editions  as  a  leading 
source  of  inaccuracy,  have  been  largely  eliminated  in  later  profiles. 
Acknowledgment  in  detail  of  indebtedness  for  this  material  would 
render  necessary  a  list  of  nearly  all  the  leading  railroad  engineers  of 
the  country,  which  want  of  space  forbids. 
Besides  the  profiles  received  directly  from  railroad  organizations, 
numerous  profiles  have  been  obtained  from  other  sources.  First 
among  these  should  be  mentioned  those  published  by  Mr.  Warren 
Upham,  in  Bulletin  No.  72  of  this  Survey,  entitled  " Altitudes  between 
Lake  Superior  and  the  Rocky  Mountains."  While  nearly  all  of  these 
profiles  had  previously  been  obtained  directly  from  the  railroads, 
many  of  those  presented  by  Mr.  Upham  have  been  used,  in  the  belief 
that  his  adjustment  of  them  is  the  most  consistent  possible. 
The  adjustment  of  railroad  levels  has  proved  a  simpler  task  than 
at  the  time  of  publishing  the  earlier  editions.  This  is  due  in  great 
part  to  the  fact  that  many  more  lines  of  precise  levels  have  been  run, 
