In  studying  the  general   relation  between   topography  and  outcrop,  the  following
generalizations  will  soon  be  made  out :

(a)   the  boundary  lines  of  horizontal  strata  run  exactly  parallel  with  the  contours;
(d)   the  boundary  lines  of  vertical  strata,  on  the  other  hand,  run  in  straight  lines
across  country  independently  of  the  contours,  in  the  direction  of  the  strike;


TOPOGRAPHY  AND  OUTCROP


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(c)  hence  the  lower  the  dip  of  the  strata  the  more  closely  will  the  outcrop  approxi-
mate in  trend  to  that  of  the  contours,  whilst  the  higher  the  dip  the  greater  the
tendency  of  the  outcrop  to  run  irrespective  of  the  contour  lines ;

(d)  the  boundary  lines  of  stratadipping  into  a  hill  are  less  winding  than  the  contours.
This  should  be  evident,  for  if  the  dip  be  increased  to  the  vertical  the  boundary  lines

of  the  strata  would  gradually  become  parallel  straight  lines,  therefore  as  the  dip  of  the


Fig.  7.   Variation  in  Width  of  Outcrop,  due  to  relation  of  dip  to  slope,   a— a'  =  outcrop,
bed  into  the  hill  increases,  the  boundary  lines  leave  the  contours  and  become  more  nearly
straight  lines.
(e)    the  boundary  lines  of  strata  dipping  out  from  a  hill  are  more  winding  than  the

contours.
This  is  the  reverse  of  the  last  generalization,  for  if  the  dip  be  increased  till  it  be  equal
to  that  of  the  slope  of  the  ground  the  boundary  lines  would  run  down  the  flanks  of  the
hill  in  parallel  lines  and  until  the  slope  varied  they  could  not  meet,  but  when  the  dip
exceeds  the  slope,  the  boundary  lines  will  begin  to  draw  in  towards  straight  lines  pro-
portionately to  the  increase  in  dip.
The  most  significant  facts  of  the  relationship  between  topography  and  outcrop  are
best  brought  out  by  the  study  of  actual  examples.
