Fig.  3. — Section  from  the  Hills  near  B  etch  am  to  the  Great  Eastern  Hallway  at  Brentwood. 
318 
ME.  H.  W.  M0NCST0N  ON  EOTTLDEES  AND 
[Aug.  1893, 
G-reat  Eastern  Bail  way 
longest  diameter.  I  had  a 
section  cut  from  it,  and  it 
proves  to  be  a  fine-grained 
dolerite,  composed  of  lath¬ 
shaped  crystals  of  plagio- 
clase  felspar,  with  here  and 
there  one  somewhat  larger 
and  broader  than  the  rest. 
There  are  several  crystals 
stained  brown  by  limonite, 
which  may  represent  a  ferru¬ 
ginous  olivine  or  a  mineral 
of  the  enstatite  group. 
There  is  nothing  very  cha- 
racteristic  about  the  rock. 
The  composition  of  the 
j!  gravel  shows  that  it  is 
4§  partly  derived  from  the 
0  south,  and  partly  from  the 
north  or  from  the  debris  of 
£  Northern  Drift.  Dartford 
§  Heath  forms  part  of  an  old 
-§  high  terrace  of  gravel,  136 
feet  O.D. ;  and  south  of 
>  the  gravel-patch  the  ground 
rises  to  above  200  feet  O.D. 
If  in  Joy  dens  Wood.  The 
A  patches  of  gravel  on  the  op- 
posite  side  of  the  Darent,  at 
£  Dartford  Brent  (131  feet 
~  O.D.),  at  Horns  Cross  (115 
T!  feet  O.D.)  and  above  Green- 
fL  hithe  (100  feet  O.D. ),  were, 
f  as  Mr.  F.  C.  J.  Spurred 
£  pointed  out  to  me  clearly, 
§  once  part  of  the  same  ter- 
§  race.  The  last  of  these 
M  patches  is  shown  in  fig.  3. 
I  have  drawn  the  line  of 
that  section  2|  miles  west 
of  Dartford  Brent,  in  order 
to  bring  in  the  Brentwood 
Shingle  of  Warley  (360  feet 
O.D.)  and  to  show  its  rela¬ 
tion  to  the  Thames  Gravels. 
The  level  and  position  of  the 
patch  of  Boulder  Clay  de¬ 
scribed  by  Mr.  T.  V.  Holmes, 
F.G.S.,1  is  shown  by  a  star. 
1  Quart.  Journ.  Geol.  Soc. 
vol.  xlviii.  (1892)  p.  365. 
