334 
EEV.  S.  HATJGHTON  ON  THE  PHYSICAL  STErCTUEE  OF  THE 
observations  of  cleavage,  joint,  and  fault  planes  here  recorded,  are  confined  to  the  sohd 
conglomerate  itself,  as  this  rock  seemed  to  me,  to  offer  a sort  of  exjpei'iraentum  cnicis 
between  the  polar  and  mechanical  theories  of  cleavage  and  joints. 
This  conglomerate  is  composed  of  numerous  rounded  pebbles,  principally  of  quartz, 
with  a few  of  slate,  and  granite  containing  white  mica,  similar  to  that  of  the  granites  of 
the  main  chain  between  Dublin  and  New  Koss  (70  miles);  the  quartz  pebbles  being 
generally  from  4 to  6 inches  in  diameter,  the  whole  cemented  together  by  a paste,  rarely 
calcareous,  containing  abundance  of  red  peroxide  of  iron,  which  gives  its  characteristic- 
colour  and  name  to  the  entire  rock. 
About  the  centre  of  the  coast  line  between  Creadan  and  Brownstown  Heads,  is  the 
promontory  of  Red  Head,  forming  the  western  entrance  into  Waterford  Harbour,  and 
remarkable  as  being  the  central  point  of  the  geological  elevation  of  the  whole  district, 
inasmuch  as  the  faults  to  the  eastward  of  Red  Head  are  accompanied  by  downthrows  to 
the  east,  while  the  faults  to  the  westward  of  Red  Head  are  accompanied  by  downthi’ows 
to  the  west.  There  are  three  distinct  kinds  of  physical  planes  observable  in  the  Old  Red 
Sandstone  conglomerate  of  this  district,  on  each  of  which  it  is  necessary  to  make  some 
remarks.  These  planes  are — 1st.  Faults;  2nd.  Joints;  3rd.  Cleavage  Planes. 
2.  Faults. 
A fault  is  a plane  of  division  in  a rock,  along  which  the  separated  portions  of  rock 
have  slipped,  either  vertically  or  horizontally,  or  both ; the  amount  of  vertical  dislocation 
is  the  downthrow,  and  the  amount  of  horizontal  displacement  is  the  heave  of  the  faidt. 
I determined  the  position,  strike,  inclination,  and  generally  the  doumthrow  of  twenty 
faults,  which  are  easily  reducible  to  several  systems,  very  well  marked,  and  having  a 
close  connexion  vrith  the  corresponding  systems  of  joint  planes  and  cleavage  planes  to 
be  described  presently.  As  some  of  these  systems  of  faults  are  at  right  angles  to  others, 
I shall  group  them  together  according  to  their  natural  relations,  as  follows: — 
System  A. 
No. 
Bearing. 
Dip. 
Downthrow. 
Locality. 
1. 
E.  10  N. 
55°  N. 
10  feet  North. 
Portnashrughaun. 
2. 
E.  5 N. 
66  N. 
North. 
Beenlea,  West. 
Mean  =7°  30'  North  of  East  (Magnetic). 
System  C. 
No. 
Bearing. 
Dip. 
Downthrow. 
Locality. 
1. 
N.  10  W. 
70  E. 
50  feet  East 
East  side  of  Red  Head. 
2. 
N.  5 W. 
90 
6 feet  West. 
Bishop’s  Cove. 
3. 
N.  0 W. 
75  W. 
20  feet  West. 
Stony  Cove. 
4. 
N.  0 W. 
Kilmaleague. 
Mean  =3°  45'  West  of  North  (Magnetic). 
