Various  maps  have  been  published  from  time  to  time  illustrating
the  character  and  source  of  the  water  supply  in  various  parts  of  the
state.  Among  the  earliest  of  these  water  maps  is  one  by  Dr.  Toner,
published  in  the  Transactions  of  the  Medical  and  Chirurgical  Faculty
of  Maryland.  This  is  really  little  more  than  a  sketch-map  showing
the  distribution  of  the  different  formations  of  the  Coastal  Plain  which
are  represented  as  differing  in  the  character  of  the  waters  which
they  bear.  The  most  exhaustive  work  on  the  waters  of  the  state  is
by  N.  H.  Darton  of  the  TJ.  S.  Geological  Survey.1  Illustrating  that
portion  of  the  paper  dealing  with  Maryland  are  three  maps  and  sev-
eral sections.     The  maps  are  entitled  respectively:

Map  of  Baltimore  Region  illustrating  features  of  underground

waters.
Map  of  a  portion  of  District  of  Columbia  illustrating  features

of  underground  waters.
Map  of  Eastern  Virginia  showing  distribution  of  underground

waters.
The  first  two  maps  use  as  a  base  the  topographic  sheets  of  the  Survey
on  the  scale  of  1:62500.  They  show  the  contours,  culture  and
drainage  of  these  maps  and  represent  the  exposure  and  approximate
catchment  area  of  the  Potomac  waters,  the  area  of  the  crystalline
rocks,  and  the  territory  underlain  by  the  Potomac  at  a  depth  greater
than  fifty  feet.  Heavy  blue  lines  across  the  sheet  indicate  the  depth
below  sea  level  of  the  contact  between  the  gravels  and  the  underlying
crystalline  rocks,  while  dotted  over  the  sheets  are  symbols  indicating
the  location  of  successful  and  unsuccessful  wells.  The  third  sheet  is
on  a  much  smaller  scale,  and  represents  the  regions  respectively  un-
derlain by  the  Chesapeake,  Pamunkey,  and  Potomac  waters,  together

1  Artesian  Well  Prospects  in  the  Atlantic  Coastal  Plain  Region.  Bull.  138
U.  S.  Geol.  Surv.,  pp.  124-161.
