dale.]  NOTE    ON    ARKANSAS    ROOFING    SLATES.  415 
#.  Black  "  slated  {clay  slate)  from  West  Caney. — This  is  not  a  pbyllite, 
but  a  clay  slate.  While  it  is  not  without  sonorousness,  its  surface  is 
lusterless  and  it  does  not  split  with  marked  facility  or  fineness.  Aggre- 
gate polarization  very  faint,  owing  to  incomplete  sericitization  of  the 
matrix.  There  is  a  noticeable  parallelism  in  the  particles,  distinguish- 
ing the  rock  from  a  shale.  The  particles  are  generally  coarse;  some 
are  visible  with  an  ordinary  magnifier.  Quartz  grains  are  as  much  as 
0.04  millimeter  in  diameter.  There  are  present  lenses  of  crypto- 
crystalline  quartz,  spherules  of  p}^rite,  and  carbonaceous  and  argilla- 
ceous material.  Although  the  hand  specimen  shows  no  effervescence 
in  cold  dilute  hydrochloric  acid,  a  chemical  analysis  would  probably 
show  the  presence  of  carbonates.  This  slate  is  of  very  doubtful  com- 
mercial value. 
3.  Dark-red  slate  (phyllite)  from  Mena,  near  Big  Forks. — The  color 
of  this  slate  is  somewhat  darker  than  that  of  the  well-known  "red 
slate"  of  Granville,  N.  Y.  It  is  sonorous  and  splits  easily.  The  sur- 
face is  not  so  smooth  as  that  of  the  slate  first  described,  and  it  is  also 
speckled  with  minute  lenses  which,  under  the  microscope,  are  found 
to  be  rhombs  measuring  from  0.1  to  0.2  millimeter  in  diameter;  these 
consist  of  chlorite  and  probably  rhodochrosite  (MnCo3),  pseudomorphic 
possibly  after  hematite  or  siderite.  The  aggregate  polarization  is 
brilliant.  Quartz  grains  range  up  to  0.025  millimeter.  Muscovite  and 
chlorite  scales  and  the  usual  hematite  pigment  are  present.  No  other 
carbonate  is  visible,  nor  is  there  any  effervescence  in  cold  dilute  hydro- 
chloric acid.  No  trace  of  false  cleavage  was  seen.  As  to  cleavability 
and  durability  this  slate  compares  favorably  with  the  Granville  ured 
slate." 
Jf.  Reddish  slate  (phyllite)  from  an  unnamed  locality. — This  is  inter- 
mediate in  color  between  the  Granville  "red  slate"  and  the  dark-red 
slate  last  described.  It  differs,  however,  from  the  latter  in  the  greater 
smoothness  of  its  cleavage  surface  and  in  the  absence  of  lenses.  It  is 
sonorous  and  splits  with  facility.  The  aggregate  polarization  is 
brilliant.  Quartz  grains  reach  0. 03  millimeter  in  diameter.  Muscovite 
and  chlorite  scales  and  hematite  pigment  are  present,  but  there  is 
no  carbonate,  and  no  effervescence  in  cold  dilute  hydrochloric  acid. 
This  is  slightly  superior  to  the  slate  last  described. 
5.  Gray -green  slate  (phyllite)  from  M.ena. — The  surface  of  this 
specimen  has  a  fine  waxy  luster,  but  is  marked  by  a  very  close  bedding 
foliation,  making  an  angle  of  13°  with  the  surface  obtained  in  split- 
ting. There  is  also  an  obscure  "  false"  or  secondary  cleavage  at  about 
40°  to  that  surface.  The  aggregate  polarization  is  brilliant  and  the 
material  is  remarkably  fine  grained  and  homogeneous.  Very  few  and 
very  minute  quartz  grains  are  present.  No  carbonate  is  present,  nor 
is  there  any  effervescence  in  cold  dilute  hydrochloric  acid.     Several 
