THE  SLATE  DEPOSITS  OF  CALIFORNIA  AND  UTAH. 
By  Edwin  C.  Eckel. 
This  paper  is  based  upon  the  results  of  field  work  by  the  writer 
during-  the  early  fall  of  1903.  Acknowledgments  must  be  made  to 
Messrs-.  W.  J.  Dingee  and  C.  H.  Dunton,  of  the  Eureka  Slate  Company, 
for  aid  extended  to  the  writer  during  his  investigation  of  the  California 
slate  deposits.  Without  the  facilities  for  close  examination  of  the 
quarries  offered  by  these  gentlemen,  and  the  cordial  cooperation  of 
all  the  officials  and  employees  of  their  company,  the  results  would  have 
been  comparatively  few. 
A  summary  of  the  more  purely  scientific  results  of  this  work  has 
been  recently  published, a  and  a  more  detailed  discussion  of  the 
economic  features,  with  maps  and  other  illustrations,  will  appear  in  a 
bulletin  of  the  United  States  Geological  Survey  on  the  slate  deposits 
and  industry  of  the  United  States. 
CALIFORNIA. 
Location  and  general  relations. — Though  roofing  slate  has  at  different 
times  been  quarried  on  a  small  scale  in  other  parts  of  California,  the 
only  important  slate-producing  area  in  the  State  is  located  in  Eldorado 
County.  The  quarries  which  have  been  opened  in  this  district  are 
located  along  a  line  running-  about  N.  15°  W.  from  Placerville,  at 
distances  of  1  to  6  miles  from  that  town.  The  location  and  geo- 
graphic and  geologic  relations  of  the  slate  deposits  and  quarries  can 
best  be  understood  by  reference  to  the  maps  included  in  the  Placer- 
ville folio  of  the  United  States  Geological  Survey.  The  workable 
roofing-slate  deposits  of  this  district  occur  in  a  belt  of  the  Mariposa 
slates,  of  late  Jurassic  or  early  Cretaceous  age.  The  quarries  which 
have  been  opened  are  all  situated  near  the  western  boundary  of  this 
belt  of  Mariposa  slates,  where  it  is  bordered  by  a  large  area  of  diabase. 
This  diabase  has  been  described  by  Lindgren  and  Turner  as  being  "of 
the  age  of  the  Mariposa  slates,  or  older."     A  number  of  linear  areas  of 
a  Eckel,  E.  C,  On  a  California  roofing  slate  of  igneous. origin:  Jour.  Geo!.,  vol.  12,  No.  1,  Feb.,  1904, 
pp.  15-29. 
Bull.  225—04 27  417 
