318  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,   1905. 
Ft.    in. 
18.  Gray  and  yellow  clay  shale 4        6 
j 7.  Gray,  fine-grained,  sandy  shale 6 
16.    Lignite  streak  and  chocolate-brown  shale \ 
15.  Gray  sandy  shale  and  soft  sandstones;   in  j  lac<  G  the  sandstone  is  ce- 
mented into  hard  rock,  forming  pr<  jecting  ledge 7 
14.  Gray  clay  shale 1 
13.  Chocolate-brown  shale 8 
12.  Lignite 1 
11.  Gray  and  yellow  clay  shale 25 
10.  Chocolate-brown  shale 2 
it.  Lignite 4 
8.  Chocolate-colored  clay  shale  with   abundant    plant   remains,  mostly 
.stein  impressions 1 
7.  tl  ray  clay  shale 3 
6.  Sandy  shah'  and  line  grained  sandstone 16 
a.  Clay  shale 4 
4.  Sandy  clay  shale 0 
3.  Gray  clay  shale 1 
2.    Lignite 9 
l.  Gray  clay  shale,  not  well  exposed,  to  river 40 
286 
The  beds  constituting  the  top  of  the  Laramie  arc  exposed  in  Sentinel  Butte,  where  the 
seel  ion  given  below  is  shown: 
Section  at  Sentinel  Butte,  North  Dakota.^ 
Ft.   i 
29.    Alternating  layers  of  highly  calcareous  gray  clay  and  very  fine-grained, 
compact,  brittle,  gray  limestone,  I'mcly  lamina  ted,  and  more  or  less 
siliceous.    Some  of  the  sandstone  beds  weather  into  thin  laminae, 
one-sixteenth  of  an  inch  thick  and  less 7 
28.   Very  calcareous  gray  clay,  weathering  to  a  greenish  color IS 
27.  Gray  hard  sandstone 40-f)0 
26.  Gray  and  yellow  sandy  clay 25 
25.  Brown  clay  and  thin  seam  of  lignite I 
24.  Gray  and  yellow  sandy  clays 48 
23.    Lignite 
22.  Soil .  fine-grained  argillaceous  sandstone L2 
21.  Brown  and  gray  clay  shale  containing  many  selenite  crystals 4 
20.  Soft,  fine-grained  sandstone I 
19.   Lignite I    I 
18.  Chocolate-brown  clay  shale,  with  carbonized  wood I 
17    Bluish-gray  clay 10 
16.  < I  ray  sand,  cemented  in  places  into  soft  sandstone 12 
L5.    Not  well  exposed,  hut  probably  Clay  shale .'»() 
14.   Lignite 
13.  Gray  sandy  clay 32 
12.  ( 1  ray  clay  shale  with  no  sand 2 
11.   Lignite 6 
10.   Sandy  clay  shale,  colored  brown  above .r> 
9.    Line  gray  sand 4 
8.  Gray  sandy  clay  shale,  containing  nodules,  similar  to  No.  6 14 
7.   Finely  laminated  sand 4 
ti.  Gray  sandy  clay  shale  with  ferruginous  bands 8 
5.  Chocolate-brown  sandy  clay  shale 1 
4.  Gray  clay  shale 
3.  Sandy  gray  clay,  containing  abundant  siliceous  iron  nodules,  arranged 
mostly  in    bands  at    certain  horizon.      These  hard   nodules   projed 
from  the  surface  of  the  softer  clay  and   also  cap  small  clay  columns.  20 
2.  Unexposed;   includes  some  sand 20 
1.  Lignite,  outcropping  in  bottom  of  ravine  nea  r  the  east  end  of  t  he  butte, 
exposed 20 
378 
N<>-.  28  and  29  of  the  above  sect  ion  are  probably  Tertiary. 
"Third  Bienn.  Kept.  Geol   Survey  North  Dakota,  pp.  165  L66. 
