Glacial  Deposits.  —  We  have  already  learned  that  glaciers  carry
with  them  great  masses  of  d^ris,  either  in  the  form  of  lateral

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ICE  DEPOSITS


and  medial  moraines  upon  their  upper  surfaces,  or  frozen  in  the
interior  of  the  ice,  or  pushed  along  beneath  it.  When  the  ice
reaches  the  end  of  the  glacier,  where  the  rates  of  motion  and
melting  balance  each  other,  all  the  burden  which  it  is  transporting
is  deposited  in  a  great  mound  or  ridge,  the  terminal  moraine.  The
terminal  moraine  is  composed  of  material  which  was  carried  upon
and  within  the  ice  and  that  which  was  pushed  along  beneath  the


Fig.  io8.  —  Fluted  ground  moraine ;  Columbia  Glacier,  Alaska.     (U.  S.  G.  S.)


glacier.  It  is  gradually  built  up  around  the  end  of  the  glacier  and
extends  up  along  its  sides  so  far  as  the  conformation  of  the  ground
will  permit  the  material  to  gather,  and  is  thus  more  or  less  crescentic,
with  concave  side  directed  upward.  Moving  ice  does  not  sort  the
material  which  it  carries,  as  flowing  water  does,  because  in  a  glacier
there  is  no  such  definite  relation  between  velocity  and  transporting
power.  Hence,  the  terminal  moraine  is  unstratified  and  is  com-
posed of  materiak  of  all  sizes,  from  dust  and  sand  up  to  great


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GLAQAL  DEPOSITS


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boulders  weighing  hundreds  of  tons,  all  mingled  together  in  con-
fusion. In  the  case  of  a  glacier  which  carries  the  principal  part
of  its  burden  upon  its  upper  surface,  the  terminal  moraine  is  chiefly
made  up  of  angular  blocks  that  have  undergone  little  or  no  abrasion,
together  with  earth,  sand,  gravel,  and  whatever  kind  of  material
the  overhanging  cliflfs  may  have  delivered  to  the  moving  ice.
