eckei,]    CEMENT-ROCK  DEPOSITS  OF  LEHIGH  DISTRICT,   PA.-N.   J.    449 
account  for  the  distribution  of  the  cement  materials  used  here.  These 
three  formations  are,  in  descending  order,  the  (1)  Hudson  shales,  slates, 
and  sandstones;  (2)  Trenton  limestone  (Lehigh  cement  rock);  (3)  Kit- 
fcatinny  limestone  (magnesian).  As  all  these  rocks  dip,  in  general, 
north-westward,  the  Hudson  rocks  occupy  the  northwestern  portion 
of  the  district,  while  the  cement  rock  and  magnesian  limestone  out- 
crop in  succession  farther  southeast. 
Hudson  shale. — This  series  includes  very  thick  beds  of  dark-gray 
to  black  shales,  with  occasional  thin  beds  of  sandstone.  In  certain 
localities,  as  near  Slatington and  Bangor,  Pa.,  and  Newton,  N.  J.,  these 
shales  have  been  so  altered  by  pressure  as  to  become  slates,  the  quar- 
rying of  which  now  supports  a  large  roofing  slate  industry. 
The  composition  of  the  typical  shales  and  slates  of  the  Hudson  for- 
mation is  well  shown  by  the  following  analyses: 
Analyses  of  Hudson  shale  and  slate  in  Pennsylvania  and  New  Jersey. 
Silica  (Si02 )....: 
Alumina  ( A1203) 
Iron  oxide  (Fe203) 
Lime  (CaO) 
Lime  carbonate  (CaC03) 
Magnesia  (MgO)  
Magnesium  carbonate  (MgC03 
Alkalies 
Carbon  dioxide  (C02) 
Water  (H20) 
Per  cent. 
68.62 
12.68 
4.20 
2.34 
3.76 
3.73 
4.47 
Per  cent. 
68.00 
14.40 
5.40 
2.68 
1.51 
.11 
2.30 
2.70 
Per  cent. 
56.60 
21.00 
5.65 
3.42 
2.30 
.50 
2.20 
3.00 
Per  cent. 
a  76.  22 
13.05 
2.67 
.93 
a  Insoluble. 
1.  East  Bangor,  Pa.,  Twentieth  Ann.  Rept.  U.  S.  Geol.  Survey,  pt.  6,  p.  436. 
2.  1  mile  northwest  Colemanville,  N.  J.    Geology  New  Jersey,  1868,  p.  136. 
3.  Delaware  Water  Gap,  N.  J.    Geology  New  Jersey,  1868,  p.  136. 
4.  Lafayette,  N.  J.    Rept.  New  Jersey  State  Geol.  for  1900,  p.  74. 
The  geographic  distribution  of  the  Hudson  shales  and  slates  in  the 
Lehigh  district  can  be  indicated  only  approximately  without  the  pres- 
entation of  a  geologic  map  of  the  area.  It  may  be  said  that  they 
cover  practically  all  of  Northampton,  Lehigh,  and  Berks  counties  north 
of  a  line  passing  through  Martins  Creek,  Nazareth,  Bath,  Whitehall, 
Ironton,  Guthsville,  Monterey,  Kutztown,  Molltown,  and  Leesport. 
As  above  noted,  the  rocks  of  the  Lehigh  district  have  a  general  dip 
to  the  northwest,  though  there  are  numerous  local  exceptions  to  this 
rule.  The  lowest  beds  of  the  Hudson  series,  therefore,  are  those 
which  outcrop  along  the  southern  boundary  of  the  formation,  as  above 
outlined.  These  lowest  beds  cany  much  more  lime  and  less  silica, 
Bull.  225—04 29 
