boutwell.]  PARK    CITY    MINING    DISTRICT,    UTAH.  143 
lies  above  a,  series  of  intercalated  limestones,  quartzites,  and  massive 
fossiliferous  limestones  of  lower  Carboniferous  age  several  thousand 
feet  in  thickness  and  it  lies  below  an  immense  thickness  of  red  shale 
of  Mesozoic  (probably  Triassic)  age.  Accordingly  the  geologic  forma- 
tions which  outcrop  within  the  Park  City  district  are  intermediate  in 
age  between  lower  Carboniferous  and  Triassic. 
The  geologic  ages  of  individual  formations  in  this  Park  City  group 
are  determined  by  means  of  distinctive  faunas  which  characterize  each 
of  the  two  limestone  formations.  Thus  the  lower  of  these  limestone 
formations,  lying  upon  the  massive  quartzite  and  beneath  the  lower 
red  shale,  contains  several  members  which  carry  faunas  indicative  of 
the  upper  Carboniferous.  The  underlying  quartzite  formation  (known 
locally  for  many  years  as  the  "  Ontario  quartzite,"  after  the  famous 
silver  mine  in  this  formation)  has  thus  far  proved  unfossiliferous.  Its 
age  may  be  closely  limited  however,  as  it  underlies  the  upper  Carbon- 
iferous limestone,  and  carries  intercalated  in  its  basal  portion  fossil- 
iferous limestones  of  lower  Carboniferous  (Mississippian)  age.  The 
upper  of  the  two  limestone  formations  bears  a  limited  but  distinctive 
fauna,  which  is  unlike  any  described  typical  fauna.  Regarding  this 
fauna,  Dr.  G.  H.  Girty  has  stated  in  a  preliminary  report  (August  11, 
1903)  on  fossils  submitted  by  the  writer  for  study  with  regard  to 
special  problems  preparatory  to  the  work  of  the  second  field  season, 
"It  now  seems  probable  that  the  fauna  will  be  correlated  with  the 
Permian  of  the  Grand  Canyon  section  *  *  *.  For  the  present  it 
seems  *  *  *  advisable  to  follow  the  usage  instituted  by  the  King 
survey,  and  to  denominate  these  beds  Permo- Carboniferous." 
The  lower  red  shale  lying  beneath  this  limestone  formation  and  on 
the  upper  Carboniferous  limestone  has  thus  far  yielded  no  remains  of 
life  and  might  be  assigned  to  the  age  of  either  of  the  inclosing  lime- 
stone formations.  Inasmuch  as  its  lithologic  aspects  are  more  charac- 
teristic of  the  overlying  formations,  however,  it  may  reasonably  be 
considered,  for  the  present,  to  be  "  Permo-Carbonif erous. "  The  upper 
of  these  two  red  shale  formations,  although  showing  a  dearth  of 
organic  life,  presents  a  normal  paleontologic  and  lithologic  transition 
from  the  underlying  "  Permo-Carbonif  erous"  (Paleozoic)  limestone  into 
the  overlying  Triassic  (Mesozoic)  sediments. 
Igneous  rocks. — Although  the  field  work  of  the  last  season  has  dis- 
closed significant  information  regarding  the  igneous  rocks  of  this 
area,  it  has  failed  to  yield  conclusive  evidence  on  the  relations  between 
the  three  recognized  types  previously  described  as  a  fine-grained  dio- 
ritic  type,  a  coarser  porphyritic  type,  and  a  poorly  defined,  variable, 
andesitic  type.  Facts  observed  both  underground  and  on  the  surface 
tend  to  suggest,  however,  that  these  are  three  closely  related  facies. 
In  case  further  study  should  show  that  they  were  derived  from  the 
same  magma  and  were  contemporaneous  or  approximately  so,  it  is  not 
