Itckel.]  SLATE    DEPOSITS    OF    CALIFORNIA    AND    UTAH.  419 
do  not  occur  in  this  quarry;  but  many  of  the  thin  quartz  seams  occupy 
this  position. 
Quartz  and  calcite  occur  in  thin  layers,  filling  joint  spaces  and  occa- 
sionally cleavage  spaces.  Pyrite  also  occurs  in  very  much  flattened 
nodules,  which  were  apparently  parallel  to  the  original  bedding. 
Character  of  the  normal  slate. — The  mass  of  the  Eureka  quarry 
product  is  a  dense,  deep-black  slate,  splitting  very  finely  and  regularly, 
with  a  smooth  glistening  surface  much  like  that  of  the  Bangor  and 
Lehigh  slates  of  Pennsylvania.  The  frequency  of  the  ribbons  and  of 
the  pyrite  nodules  prevents  the  slate  from  being  serviceable  as  mill 
stock,  but  as  a  roofing  material  it  is  excellent. 
A  specimen  of  the  black  slate,  free  from  ribbon,  was  selected  for 
analysis  in  the  laboratory  of  the  United  States  Geological  Survey. 
The  results  of  this  analysis,  by  Mr.  W.  T.  Schaller,  follow: 
Analysis  of  black  slate,  Eureka  quarry,  Slatington,  Oil. 
Per  cent. 
Silica  (Si02) 63.  52 
Alumina  ( A1203)  and  titanic  oxide  (Ti02) 16.  34 
Iron  oxides  ( FeO,  Fe203) , 6.  79 
Lime  (CaO) 98 
Magnesia  (MgO) 2. 50 
Carbon  dioxide  (C02)1                                                                                 .  8fi 
Water J 
Eureka  quarry  green  slate.0, — A  band  of  green  slate  several  feet  in 
width  crosses  the  Eureka  quarry.  On  examination  it  is  found  that 
the  borders  of  this  band  are  not  parallel  to  the  "ribbon"  of  the  black 
slate.  The  green  band  can  not,  therefore,  be  interbedded  with  the 
black  slates.  The  probability  that  it  represents  a  dike  of  massive 
igneous  rock  which  has  been  changed  into  a  slate  by  pressure  subse- 
quent to  its  intrusion  is  strengthened  when  the  chemical  composition 
of  the  green  slate  is  considered.  Two  analyses  of  the  green  slates  are 
presented  on  the  next  page.  The  first  is  of  a  sample  selected  by  the 
writer  and  analyzed  in  the  laboratory  of  the  United  States  Geological 
Survey  by  Mr.  W.  T.  Schaller;  the  second  was  given  by  Mr.  C.  H. 
Dunton,  manager  of  the  Eureka  quarry,  but  the  name  of  the  analyst 
is  unknown.  As  the  analyses  show  a  close  agreement  in  essential 
features,  it  is  probable  that  the3r  are  fairly  representative  of  the  com- 
position of  the  green  slates,  and  that  their  average,  which  is  given 
in  the  third  column  of  the  table,  may  be  regarded  as  typical  of  this 
interesting  and  apparently  unique  type  of  roofing  slate. 
a  For  a  more  detailed  discussion  of  this  interesting  "igneous  slate"  the  reader  is  referred  to  the  paper 
by  the  writer  in  the  Journal  of  Geology,  vol.  12,  1904,  pp.  15-29. 
