488  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1004.         [bull.  260. 
slate.  Each  slate  district  will  there  be  treated  according  to  the  fol- 
lowing method :  After  a  brief  geologic  account  of  the  deposit  the  slate 
will  be  described  physically  and  microscopically  and  the  results  of 
such  chemical  analyses  and  physical  tests  as  are  available  will  be 
added.  These  descriptions  will  thus  afford  a  scientific  basis  for  com- 
parative estimates  of  the  various  slates.  There  will  also  be  chapters 
on  the  classification  and  origin  of  slate,  the  present  state  of  science  on 
roofing  slates,  the  structure,  geology,  chemistry,  and  economic  geology 
of  slate,  together  with  a  bibliography.  About  two-thirds  of  the 
writer's  paper  on  the  slate  belt  of  eastern  New  York  and  western 
Vermont,  published  in  Part  III  of  the  Nineteenth  Annual  Report 
(1899),  is  to  be  carefully  revised  and  republished  in  this  bulletin, 
together  with  the  material  collected  during  a  study  of  the  Slatington 
quarries  in  1902  and  the  trips  referred  to  above.  As  stated,  this  bul- 
letin will  also  contain  papers  by  other  geologists  on  the  slates  of  Cali- 
fornia, Utah,  and  other  States,  and  will  thus  serve  as  a  reference 
work  on  the  subject. 
