348 
EEV.  S.  HATJGHTON  ON  WATEEEOED  OLD  EED  SAXDSTONE. 
First  Conjugate  System. 
A. 
629-r81 
7 46  North  of  East. 
C. 
341 -r49 
6 57  West  of  North. 
Angle  between  Axes  from  East  to  North  =89°  11^ 
Second  Conjugate  System. 
A'. 
452§-M35 
33  31  North  of  East. 
C'. 
l663-f-  47 
35  23  West  of  North. 
Angle 
between  Axes  from  East  to  North  =91°  52' 
Third  Conjugate  System. 
A". 
427-;-14 
30  30  South  of  East. 
C". 
350-;-12 
29  10  East  of  North. 
Angle  between  Axes  (North  and  East)  =91°  20' 
Fourth  Conjugate  System. 
A'". 
C'". 
One  observation. 
57°-i-6 
10  South  of  East. 
9 30  East  of  North. 
Angle  between  North  and  East  Axes  =90°  30' 
Note  added  aftee  the  reading  of  the  Paper. 
Throughout  this  paper  I have  assumed  the  perpendicularity  of  the  cleavage  planes  to  the  lines  of  maximmu 
force.  This  assumption  I have  made  on  evidence  quite  distinct  from  the  facts  mentioned  with  relation  to 
the  perpendicularity  of  the  horizontal  traces  of  the  cleavage  and  joint  planes  to  each  other.  I believe  the 
proper  evidence  of  the  perpendicularity  of  cleavage  to  the  lines  of  maximmn  force  must  be  sought  for  in 
fossHiferous  slate  districts,  where  the  distortion  of  the  fossil  enables  us  to  determine  the  exact  position  of 
the  line  of  maximum  force,  and  consequently  its  relation  to  the  plane  of  cleavage. 
The  evidence  of  fossils  is  wanting  in  the  conglomerate  of  the  County  of  Waterford,  and  we  ai-e  conse- 
quently unable  to  determine  the  precise  lines  of  maximum  force,  except  so  far  as  the  inclination  of  the  beds 
gives  us  information. 
Having  established  by  observation  the  existence  of  conjugate  systems  of  planes,  I have  drawn  mechanical 
inferences,  founded  on  the  assumption  of  the  perpendicularity  of  cleavage  to  the  lines  of  maximum  force ; 
and  these  inferences  have  not,  of  course,  the  same  degree  of  evidence  in  their  favour  that  the  geometrical 
relations  of  the  cleavage  and  joint  planes  have. 
In  fact,  the  geometrical  relations  of  these  planes  are  observed  facts,  while  the  mechanical  inferences  have 
only  the  probability  (in  my  opinion  a high  one)  of  the  law  assumed  on  other  evidence. 
