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THE    RECENT    GEOLOG 


OF 


CORNWALL 


^Extracted  from  the  Geological  Magazine,  from  January  to  July,  1879. 
Trubner  &  Co.,  57  and  59,  Ludgate  Hill,  London. 


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IL. 


THE    RECENT    GEOLOGY 

OF 

CORNWALL. 


VV.  A.  B.  IJSSHER,  ESQ.,  F.G.S., 


or    H.  M.  GEOLOGICAL  SURVEY. 


[Extracted  from  the  Geological  Magazine,  from  January  to  July,  1879.] 


CONTENTS. 


PART  I. 

HiSTOKICAL         1 

Paut  1.     Contemporary  Observations  2 

Pakt  2.    Records  of  Disastrous  Inundations  4 

Part  3.     Traditions  of  the  Lyonesse,  etc 6 

Part  4.     St.  Michael's  Mount 10 

Appendix    16 

PART  II. 

Post-Tertiary  Geology  of  Cornwall  17 

1.  Oldest  Superficial  Deposits     17 

Notes  on  Glacial  Hypotheses 24 

PART  III. 

The  Raised  Beaches  and  Associated  Deposits  of  the  Cornish  Coast  25 

General  Conclusions  37 

PART  IV. 

Submeeged  Forests  and  Stream-tin  Gratels  40 

Stream  Tin  Sections    42 

General  Notes      50 

PART  V. 

Blown   Sands   and   Recent   Marine.     Notes   on  Blown  Sands   and 

Gravel  Bars 53 

General  Notes 66 


THE 

POST-TERTIARY    GEOLOGY  OF 
CORNWALL. 


PART    I.     HISTORICAL. 


TO  ascertain  the  most  recent  movement  to  which  a  country  has 
been  subjected,  and  by  careful  comparison  with  the  past  to 
discover  what  insensible  changes  are  now  progressing,  is  of  the 
utmost  im^jortance  in  approaching  its  Quaternary  History. 

By  a  recourse  to  such  occasional  observations  as  have  been  re- 
corded by  historians  or  monkish  chroniclers,  gleaned  perhaps  in 
few  cases  from  actual  investigation,  and  exaggerated,  no  doubt, 
in  an  age  delighting  in  the  marvellous,  some  information  may  be 
gained ;  but  when  we  consider  that  these  notes  were  made  rather 
for  the  gratification  of  the  curious  than  with  a  view  to  ascertain 
their  causes  or  to  forecast  their  effects,  and  that  the  facts  of  one 
century  may  become  the  legends  of  the  next,  it  behoves  us  to 
sift  the  evidence,  retaining  only  such  bare  and  unvarnished  state- 
ments as  by  incidental  mention  and  simple  relation  appear  most 
worthy  of  credence,  especially  when  the  accounts  are  corroborated 
by  independent  writers. 

It  has  ever  been  the  characteristic  of  the  ignorant  and  unin- 
quiring  peasantry  to  ascribe  the  occurrence  of  great  boulders  of 
rock  dissimilar  to  any  in  the  neighbourhood,  the  fantastic  shape, 
BO  frequently  effected  by  weathering  in  rocks  of  unequal  durability 
and  such-like  remarkable  objects,  to  the  agency  of  fabulous  beings 
endowed  with  enoruious  strength  and  gigantic  proportions ;  and  so 
names  are  given  to  phenomena  of  unusual  occurrence,  and  are 
retained  by  a  less  credulous  posterity  even  when  the  legends  which 
suggested  them  have  almost  entirely  passed  away.  Many  such  names 
are  to  be  met  with  in  Cornwall. 

Again,  traditions  of  a  more  extensive  coast-line,  of  lands  now 
swept  away,  have  been  handed  down,  doubtless  magnifying  the 
extent  of  the  ancient  land,  as  the  account  passed  through  succeeding 
generations. 

1 


2  W.  A.  E.  UssJier — Ilktorical  Geology  of  Conmall. 

Our  familiarity  with  the  causes  producing  sucli  phenomena  as 
earthquakes,  comets,  eclipses,  and  the  like,  however  seldom  some 
of  them  have  been  experienced  in  a  lifetime,  renders  the  obser- 
vations of  the  i^resent  age  more  aocui'ate  and  less  liable  to  exaggera- 
tion than  those  of  preceding  centuries,  when  anything  of  infrequent 
occurrence  in  the  experienced  operations  of  nature  was  regarded 
as  cataclysmal,  resulting  from  direct  interposition  in  an  unvarying 
state  of  things.  The  rapid  advance  and  more  general  cultivation  of 
scientific  research,  no  longer  fettered  by  ignorance  and  superstition, 
embraces  in  an  ever-extending  chain  of  cause  and  effect  phenomena 
which  our  ancestors  regarded  as  supernatural. 

It  is  however  curious  to  note  how  some  amongst  the  ancients, 
by  the  acuteness  of  their  perceptions,  grasped  an  occasional  scientific 
truth  which  has  been  corroborated  in  the  present  day.  Thus,  it  is 
remarkable  that  Ovid,  Pj'thagoras,  Pliny,  and  Aristotle  shoukl  have 
believed  the  sea  to  be  less  changeable  than  the  land.'  Strabo,  in 
opposing  the  opinions  of  Eratosthenes  and  Xanthus  as  to  the  cause 
of  shells  being  found  at  great  elevations  and  distances  from  the 
sea,  says  :  "  It  is  not  because  the  lands  covered  by  the  seas  were 
originally  at  different  altitudes  that  the  waters  have  arisen  or 
subsided  or  receded  from  some  parts  and  inundated  others.  But 
the  reason  is  that  the  same  land  is  sometimes  raised  up  or  de2jressed, 
so  that  it  either  overflows  or  returns  to  its  own  place  again.  We 
must  therefore  ascribe  the  cause  to  the  ground,  either  to  that  ground 
which  is  under  the  sea  or  to  that  which  becomes  flooded  by  it,  but 
ratlier  to  that  which  lies  beneath  the  sea,  for  this  is  more  movable." 

The  historical  evidence  may  be  classified  under  three  heads  : — 

Firstly,  accounts  of  unusual  disturbances  of  the  sea  by  contem- 
porary observers. 

Secondly,  records  of  disastrous  inundations  preserved  in  old 
chronicles. 

Thirdly',  traditions  of  the  Lyonesse  and  probable  references  of  the 
ancient  geogra2)hers  and  historians  to  the  Scilly  Isles. 

Fourthly,  the  insulation  of  St.  Michael's  Mount  and  the  identifi- 
cation of  Ictis. 


Part  1. —  Contemporary  Observations. 

These  have  been  taken  exclusively  from  papers  by  Mr.  Edmonds. 
In  Edin.  New  Phil.  Journ.  he  mentions  an  influx  and  reflux  of  the 
sea,  varying  from  three  to  above  five  feet,  in  Mounts  Bay,  at  five  p.m., 
on  March  23rd,  1847;  the  double  movement  taking  from  fifteen  to 
twenty  minutes.  During  the  most  part  of  the  day  the  water,  from 
the  mouth  of  the  Catwater  to  within  Sutton  Pool,  at  Plymouth, 
was  constantly  agitated  by  flux  and  reflux. 

In  Falmouth  Harbour,  and  on  the  shores  of  the  Scilly  Isles, 
similar  oscillations  took  place,  whilst  in  St.  Ives  Bay  nothing  un- 
usual was  remarked. 

1  Stoddart,  Troc.  Rrist.  Nat.  Soc.  for  1870,  vol.  v.  p.  43. 


W.  A.  E.  Ua-slier — Historical  Geologi/  of  Cornwall.  3 

At  Newlyn  four  fluxes  and  refluxes  of  the  sea  occurred  in  an  hour 
and  a  half.  In  the  shallow  water  between  Marazion  and  Penzance 
no  agitation  was  perceptible.  The  limits  of  the  disturbance,  so  far 
as  observed,  were  from  Mousehole  on  the  west  to  Porthleven  on  the 
east,  a  distance  of  ten  miles. 

On  October  30th  of  the  same  year,  at  five  p.m.,  a  rise  of  the  sea, 
coming  from  the  south-west,  and  reaching  five  feet,  took  place  at 
Penzance. 

Three  similar  fluxes  and  refluxes  occurred  at  Plymouth  in  forty 
minutes. 

Four  whirlwinds,  accompanied  by  shocks,  passed  through  the 
parish  of  St.  Just,  on  December  12th,  1846. 

The  same  writer'  mentions  an  earthquake  felt  over  100  miles, 
from  the  Soilly  Isles  through  Cornwall  as  far  as  Plymouth,  in 
July,  1757. 

A  disturbance  of  the  sea  took  place  in  Mounts  Bay  at  four  hours 
and  a  quarter  after  the  great  earthquake  at  Lisbon  in  1755,  when 
the  sea  suddenly  rose  to  the  height  of  six  feet  at  St.  Michael's 
Mount,  coming  in  from  the  S.E. ;  and  to  eight  feet  at  Penzance 
Pier,  coming  in  from  the  S.E.  and  S.S.E.  At  Newlyn  Pier  and 
Mousehole  the  sea  coming  in  from  the  south  rose  and  fell  ten  feet. 
Toward  the  decline  of  the  commotion,  tlie  sea  was  found  to  be 
running  at  seven  miles  an  hour  in  Guavas  Lake. 

If  the  observation  recorded  in  the  following  extract  be  not  mag- 
nified in  transmission  from  the  original  observe!',  it  shows  the  care 
necessary  in  ascribing  the  occurrence  of  some  isolated  pebbles  and 
boulders  above  the  reach  of  the  highest  spring  tides  to  changes 
in  the  relation  of  sea  and  land :  "  I  have  been  informed  by  two 
descendants  of  an  eye-witness  that  at  Lamorna  Cove,  which  is  on 
the  south-east  part  of  Mounts  Bay,  the  sea  on  this  occasion  rushed 
suddenly  towards  the  shore  in  vast  waves  with  such  impetuosity 
that  large  rounded  blocks  of  granite  from  below  low-water  mark 
were  swept  along  like  pebbles,  and  many  were  deposited  far  above 
high-water  mark.  One  of  seven  or  eight  tons  weight  was  rolled 
to  and  fro  several  feet  above  high-tide  level." 

Whether  the  size  of  the  boulders  be  exaggerated  or  not,  it  is 
evident  that  the  disturbance  described  was  sufficiently  powerful 
to  shift  large  stones  from  the  existing  beach  to  a  point  about  the 
average  height  of  the  Cornish  raised  beaches  above  high-water 
mark,  even  allowing  for  an  exaggeration  of  five  feet  in  the  height 
to  which  the  large  boulder  was  said  to  be  moved.  At  Polkerris, 
near  the  Par  estuary,  "  Raised  Beach "  has  been  engraved  on  the 
map,  apparently  on  the  strength  of  the  occurrence  of  isolated  quartz 
pebbles  amid  sandy  debris  on  a  small  promontory  some  twenty  feet 
above  the  adjacent  beach,  which  is  composed  of  exactly  similar  quartz 
pebbles.  This  phenomenon  is  much  more  likely  to  have  been 
produced  by  exceptional  gales,  or  such  disturbances  as  have  been 
described,    than   to   be   the    relics   of  a   raised   beach,   the  lighter 

»  T.  R.  G.  S.  Corn.,  vol.  vii.  p.  IGl,  etc. 


4  W.  A.  E.  Ussher — Histo)'ical  Geology  of  Cornwall. 

materials  of  which  had  been  dissipated  by  spray  and  rain,  for  the 
raised  beaches  are  usually  too  much  consolidated  to  allow  of  such 
facile  dissipation. 

In  February,  1759,  Mr.  Edmonds  records  a  slight  shock  felt 
at  Liskeard  for  fifteen  minutes,  accompanied  hy  blood-red  rays. 

In  March,  17G1,  on  the  day  of  the  second  earthquake  at  Lisbon, 
the  sea  advanced  and  retreated  five  times  four  hours  and  a  quarter 
after  ebb-tide,  at  five  p.m.,  in  Mounts  Bay,  rising  six  feet  at 
Penzance  and  Newlyn,  and  four  feet  at  St.  Michael's  Mount.  At 
the  Scilly  Isles  the  agitation  continued  for  more  than  two  hours. 

In  July,  1761,  fluxes  and  refluxes  occurred  in  Mounts  Bay,  and 
at  Falmouth,  Fowey,  and  Plymouth. 

In  1789  fluxes  and  refluxes  of  the  sea  were  observed  at  Penzance 
and  St.  Michael's  Mount.  Earth  shocks  were  felt  on  December 
30th,  1832. 

In  1836  a  slight  disturbance  of  the  earth  was  felt  in  the  parishes 
of  Budock  and  Stithians. 

On  October  20th,  1837,  a  slight  shock  is  said  to  have  been  felt  in 
the  Scilly  Isles. 

On  February  17th,  1842,  an  earthquake  was  felt  between  the 
hours  of  eight  and  nine  a.m.,  from  Manaccan  on  the  south  to  St. 
Cubert  on  the  north,  a  distance  of  twenty-five  miles ;  and  from 
Falmouth  on  the  east  to  St.  Hilary  on  the  west,  a  distance  of 
eighteen  miles. 

On  July  oth,  1843,  the  sea  was  much  agitated  within  Porthleven 
Harbour.  Three  hundred  j^ards  from  the  north  shore  of  the  harl)our 
nothing  unusual  was  observed.  At  one  p.si.  the  sea  rushed  in 
for  fifty  yards,  reaching  a  height  of  four  or  five  feet  at  Marazion. 
At  Penzance  an  agitation  accompanied  by  strange  currents  was 
observed. 

The  eiFects  of  the  disturbances  above  cited  are  eminently  tran- 
sient, except  in  abnormal  shifting  of  detritus  to  higher  levels,  but 
when  we  find  that  within  the  short  space  of  a  century  Cornwall 
has  felt  the  spent  force  of  earthquakes  propagated  from  distant 
centres  of  internal  or  eruptive  motion,  the  probability  of  similar 
disturbances  emanating  from  much  nearer  sources,  and  productive  of 
considerable  if  not  jiermanent  effects,  is  at  once  suggested.  Whilst 
the  record  of  such  cataclysms  in  early  historic  or  mediasval  times 
would  refer  to  their  disastrous  effects,  want  of  knowledge  and 
observation  leaving  the  causes  unknown,  the  recent  prehistoric 
geological  period  conceals  them  in  an  impenetrable  veil. 


Part  2. — Eecords  of  Disastrous  Inundations. 

I  quote  the  following  from  Mr.  Peacock's  book  (On  Vast  Sinkings 
of  Land,  etc.)  : — 

p.  116,  "Dr.  Barham  quotes  from  the  Saxon  Chronicle,  par- 
ticulars of  the  inundation  of  Nov.  11th,  1099  ;  and  of  another  on 
the  same  authority  in  1014.     This  year  (1014)  on  Michaelmas  Eve, 


W.  A.  E.  Ussher — Historical  Geology  of  Cornwall.  5 

Sept.  2Sth,  came  the  great  sea-flood  whicli  spread  over  this  land, 
and  ran  up  as  far  as  it  never  did  before,  overwhelming  many  towns 
and  an  innumerable  multitude  of  people." 

p.  115.  An  account  of  a  destructive  inundation  13  years  after 
the  Domesday  Survey,  by  Florence  of  Worcester ;  "  On  the  3rd  day 
of  the  Nones  of  November  1099,  the  sea  came  out  upon  the  shore, 
and  buried  towns  and  men  very  many,  and  oxen  and  sheep 
innumerable."  From  the  Saxon  Chronicle  for  that  year,  "  On  St. 
Martin's  mass  da3^  the  11th  Nov.,  sprung  up  so  much  of  the  sea- 
flood,  and  so  myckle  harm  did,  as  no  man  minded  that  it  ever  afore 
did,  and  there  was  the  ilk  day  a  new  moon."  "Whence,"  says  Mr. 
Peacock,  "  the  catastrophes  cannot  be  referred  to  the  great  height 
of  the  tide,  for  the  highest  spring-tides  do  not  occur  until  several 
tides  after  tlie  new  moon,  and  the  11th  of  November  is  several 
weeks  after  the  equinox." 

p.  138.  Mr.  Peacock  accounts  for  Geoifery  of  Monmouth's 
omission  of  the  mention  of  the  inundations  of  1014  and  1099,  on 
the  ground  that  the  chroniclers  very  often  omitted  to  record  the 
actual  disappearances  of  lands. 

In  p.  140  he  quotes  from  Mr.  Pengelly's  paper  on  the  Antiquity 
of  Man  in  the  South- West  of  England  :  "  Leland  (1533-1540)  says, 
'  Ther  hath  been  much  land  devourid  betwixt  Pensandes  and  Mouse- 
hole.     Ther  is  an  old  legend a  Tounlet  in  this  Part  (now 

defaced  and)  lying  under  the  water,'  " 

In  p.  141  he  gives  a  reference  to  Mounts  Bay  from  Magna 
Britannia  published  anonymously  in  1722  (vol.  i.  p.  308)  :  "Tis  a 
tradition  among  the  people  here,  that  the  ocean  breaking  in  violently, 
drowned  that  part  of  the  country  which  now  is  the  Bay."  Mr. 
Peacock  disposes  of  the  idea  that  the  catastrophes  of  1014  and 
1099  might  have  been  the  result  of  similar  movements  to  those 
"which  occurred  on  the  Soutli  Coast  of  England  in  1817,  1824,  and 
1859,  at  a  considerable  distance  of  time  from  either  equinox,"  on 
account  of  the  unprecedented  harm  done  by  them,  and  the  in- 
adequacy of  such  high  tides  as  those  mentioned  to  produce  com- 
mensurate effects. 

Notwithstanding,  I  am  inclined  to  differ  from  Mr.  Peacock  in  this 
conclusion  for  the  following  reasons  : — 

Firstly.  Such  traditional  accounts  as  those  of  Leland  and  the 
Magna  Britannia,  and  the  statement  of  Vice-Adrairal  Thevenard  in 
Mem.  relatifs  a  la  Marine  (a.d.  1800),  "La  submersion  du  terrain 
.  .  .  et  de  la  pointe  ouest  de  I'Angleterre.  ix."  (commencement  of 
ninth  century),  quoted  by  Mr.  Peacock  in  p.  88  of  his  book,  must  be 
laid  out  of  the  question. 

Secondly.  All  statements  made  by  writers  who  lived  long  after  the 
occurrences  they  describe  must  be  accepted  with  reservation,  as  they 
may  have  been  derived  from  the  contemporary  record  of  the 
occurrence,  and  cannot,  therefore,  be  said  to  furnish  additional 
evidence.  Thus  with  Florence  of  Worcester,  who  wrote  in  the 
thirteenth  century. 

Thirdly.    Taking  the   Saxon  Chronicle  as  the    only  direct   con- 


6  W.  A.  E.  Un'-ihcr — Jl'mtorical  Givlo'jij  of  Cunnvall. 

temporar}'  account  of  the  inundations  of  the  eleventh  century,  one 
would  like  to  know  whether  the  descriptions  there  given  were  penned 
by  an  eye-witness  of  the  catastrophe,  or  inserted  from  rumours  which 
would  doubtless  have  magnified  the  disaster  ere  they  reached  the 
chronicler. 

Fourthly.  Admitting  Mr.  Peacock's  reason  for  the  omission  of 
remarkable  events  here  and  there  by  the  chroniclers  generally,  I 
cannot  see  their  particular  application  to  Geofi'ery  of  Monmouth, 
who  flourished  in  the  twelfth  century,  and  would  therefore  have  less 
excuse  for  omitting  to  mention  events,  which  had  been  witnessed 
b}''  the  generations  immediately  preceding  him,  than  Florence  of 
Worcester,  who  lived  more  than  three  centuries  after  they  had  occurred. 
For  these  reasons  I  am  disinclined  to  believe  in  sudden  elevations  or 
depressions  of  land,  and  to  consider  that,  owing  to  some  such  dis- 
turbances as  I  have  quoted  from  I\Ir.  Edmonds,  though  perhaps  of 
greater  magnitude,  lives  may  have  been  lost  and  lands  devastated  by 
the  influx  of  waves  propagated  by  earthquake  shocks,  and  by  seasons 
of  unjirecedented  flood.  That  the  eftects  produced  would  be  partial 
or  transient,  whilst  the  story  of  the  disaster  for  which  men  could 
assign  no  cause  would  be  magnified  as  it  2:)assed  from  the  eye- 
witnesses of  the  catastrophe  to  their  descendants,  and  finally,  with 
many  interpolations  and  distortions,  live  as  a  local  tradition  with 
perhaps  very  little  of  its  original  significance  remaining. 


Part  3. — Traditions  of  tlte  Lijonesse,  d-c. 

The  following  information  is  chiefly  extracted  from  Mr.  Peacock's 
book  : — 

"It  is  said  that  in  Camden's  time  the  inhabitants  of  Cornwall 
were  of  opinion  that  the  Land's  End  did  once  extend  further  to  the 
west,  which  the  seamen  positively  conclude  from  the  rubbish 
they  draw  up,  and  that  the  land  there  drowned  by  the  incursions  of 
the  sea  was  called  Lionesse.  That  a  place  within  the  Seven  Stones 
is  called  by  the  Cornish  people  Trevga  (i.e.  a  dwelling),  and  that 
windows  and  other  such  stuff  have  been  brought  up  from  the  bottom 
there  with  fish-hooks,  for  it  is  the  best  place  for  fishing.  That  at 
the  time  of  inundation  supposed  Trevelyan  swam  from  thence  (at 
least  15  nautical  miles  to  the  nearest  jiart  of  the  mainland)  and  in 
memory  thereof  bears  Gules,  an  horse  Argent  issuing  out  of  the  sea 
proper."     {Vide  Note  A.) 

"  If  the  Lyonesse  countrj'  really  existed  in  Ptolemy's  time 
(a.d.  117  to  161),  it  cannot  have  extended  as  far  westwards  as  is 
shown  on  the  map  in  the  Churchman's  Magazine  (for  July,  1863, 
p.  39),  from  Land's  End  and  Lizard  Point  to  and  comprising  the 
Scilly  Isles.  Because  Strabo,  who  flourished  at  least  a  century 
before  Ptolemy,  quoting  Posidonius,  who  was  still  older,  mentions 
those  islands  as  then  existing  under  the  name  of  Cassiterides  (book  iii. 
cap.  ii.  §  9),  and  that  they  were  ten  in  number  {Ibid.  cap.  v.  §  11)." 

"  Dr.  Paris,  in  his  '  Guide  to  Mounts  Bay  and  the  Lands  End.' 


W.  A.  E.  Ussher — Historical  Geology  of  Cornwall.  7 

p.  91,  mentions  Camden's  tradition  of  the  Lyonesse  (the  Silurian 
Lyonois),  said  to  have  contained  140  parish  churches,  all  of  which 
were  swept  away  by  the  ocean."  He  says  further  that  the  Scilly 
Isles  are  now  1-40  in  number,  though  only  six  are  inhabited, 

Camden  (Britannia,  edit.  1722)  says,  "  The  Scihy  Isles  are  called 
by  Antoninus,  Sigdeles  ;  by  Sidpitius  Severus  (died  a.d.  420), 
Silliufe;  by  Solinus,  Silures;  by  Dionysius  Alexandrinus,  Hesperides; 
by  Festus  Avienus  (latter  part  of  fourth  century),  Ostrymnides ;  by 
several  Greek  writers,  including  Diodorus,  and  by  Pliny  the  Elder, 
Cassiterides."  ' 

Dr.  Borlase,-  in  a  letter  to  the  Eev.  J.  Birch  on  the  Scilly  Isles,  says 
that  the  present  inhabitants  are  new  comers,  having  no  connexion 
with  the  old  race,  as  all  the  antiquities  found  in  the  islands  belong 
to  the  rudest  Druidic  times. 

In  isles  now  uninliabited  and  not  used  for  pasturage,  rude  stone 
pillars,  erect  circles  of  stone,  kistvaens,  innumerable  rock  basins, 
and  tolmens.^  are  found,  whilst  the  small  islands,  tenements,  and 
creeks,  are  called  by  British  names. 

Within  the  three  years  previous  to  1753,  he  states  that  the  ad- 
vance of  the  sea  in  the  Scilly  Isles  has  been  very  considerable ;  this 
advance  being,  in  his  opinion,  due  to  subsidence  for  the  following 
reasons  :  Strabo's  opinion  as  to  their  number  {vide  supra)  and  as  to 
one  only  being  desert  and  uninhabited  ;  the  fact  that  the  Isle  of 
Scilly,  which  gives  its  name  to  the  group,  is  now  a  high  barren 
rock,  a  furlong  across,  with  cliffs  to  which  only  sea-birds  can  obtain 
access. 

The  flats  which  stretch  from  one  island  to  another  are  plain 
evidences  of  a  former  union  between  many  now  distinct  islands. 
The  flats  between  the  islands  of  Trescan,  Brehar,  and  Sampson,  are 
left  quite  dry  at  a  spring-tide  low- water,  when  walls  and  ruins  have 
frequently  been  seen  through  the  shifting  sands,  covered  by  10  to  20 
feet  of  water  at  high  tide.  As  these  foundations  were  probably  at 
one  time  six  feet  at  least  above  high-water  mark,  the  advance  of  the 
sea  by  denuding  action  alone  would  be  insufficient  to  account  for 
their  present  position,  "ten  feet  below  high- water."  Whence  he 
considers  that  "a  subsidence  amounting  to  16  feet  at  least  has  taken 
place,  which  caused  the  desertion  of  the  islands  by  their  terrified 
aboriginal  inhabitants.  These  original  inhabitants  carried  on  a  trade 
in  tin  with  the  Phoenicians,  Greeks,  and  Eomans  "  (for  this  opinion 
he  cites  Diodorus  Siculus,  lib.  v.  cap.  ii.  and  Strabo,  Geog.  lib.  iii.). 
"  Whilst  only  one  inconsiderable  vein  of  tin  occurs  in  Tresco 
Island,  and  that  betrays  no  sign  of  ancient  working,  nor  are  any  old 
workings  now  visible  sufficient  to  have  maintained  a  trade  in  tin." 
He  says  further,  "But  though  there  are  no  evidences  to  be  depended 

1  Peacock,  p.  109. 

"  Phil.  Trans,  for  1753,  vol.  48,  p.  326. 

'  Tolmens.— Oval  or  spheroidal  rocks,  when  resting  on  two  others,  with  a  cavity 
between,  are  called  by  Dr.  Borlase  tolmens  (stones  with  holes),  and  are  supposed  by 
him  to  have  been  rock  deities  (Came  on  the  Scilly  Isles). — T.R.G.S.  Corn.  vol.  vii. 
p.  144. 


8  W.  A.  E.  Uiss/ier — Historical  Geology  of  Cornuall. 

on  of  any  ancient  connexion  of  the  Land's  End  and  Scilly,  yet  that 
the  cause  of  that  inundation  which  destroyed  much  of  these  islands 
might  reach  also  to  the  Cornish  shores,  is  extremely  probable,  there 
being  several  evidences  of  a  like  subsidence  of  the  lands  in  Mounts 
Bay." 

I3r.  Borlase,  in  his  Natural  History  of  Cornwall/  says,  "The  supply 
of  tin  from  Gades  and  Spain  being  too  small  to  supply  the  vast  trade 
as  far  as  India,  they  must  have  got  it  to  the  east  of  the  Damnonii." 

The  Chaldeans  and  Arabians  call  tin  by  a  name  similar  to  the 
Greek  Kaaacrepo'i.  The  Scilly  Isles  were  called  Cassiterides 
long  before  the  Greeks  knew  of  their  position,  for  Herodotus 
(b  c.  400)  says,  Oijre  vj]crov<;  olha  KaacnTepLha<i  iovcra'i,  eK  twv  6 
Kaaairepo<;  rj/xlv  (^otra  (book  iii.  cap.  115). 

Solinus  calls  them  Insnlfe  Silurum  or  Insula  Silura,  perhaps  in 
mistake  for  islands  off  the  Welsh  coast. 

Tacitus^  says  the  Silures  were  opposite  to  Spain,  which  would 
point  to  the  Scill}^  Isles.  It  is  probable  that  the  Phoenicians  re- 
garded West  Cornwall  as  an  island,  and  one  of  the  Cassiterides,  as 
tlie  Scilly  Isles  alone  would  have  been  totally  insufficient  to  afford 
the  supply. 

"  Ortelius,^  therefore,  not  without  reason,  makes  the  Cassiterides 
to  include,  not  only  the  Scilly  Isles,  but  also  Devonshire  and 
Cornwall." 

"  Tin  was  also  anciently  found  in  Lusitania  and  Gallicia."  * 

Mr.  H.  Boase-^  quotes  Carew'^  as  follows  : — "  The  encroaching  sea 
hath  ravined  from  it  the  whole  country  of  Lionnesse,  together  with 
divers  other  parcels  of  no  little  circuit,  and  that  such  a  Lionnesse 
there  was,  these  proofs  are  yet  remaining.  The  space  between  tbe 
Land's  End  and  the  Isles  of  Scilly,  being  about  30  miles,  to  this  day 
retaineth  that  name,  in  Cornish,  Lethowsow,  and  carrieth  an  equal 
depth  of  40  or  GO  fathoms,  save  that  about  midway  there  lieth 
a  rock  which  at  low  water  discovereth  its  head.  They  term  it  the 
Gulf,  suiting  thereby  the  other  name  of  Scilla.  Fishermen  also 
casting  their  hooks  thereabouts,  have  drawn  up  pieces  of  doors  and 
windows."  After  touching  on  Dr.  Borlase's  views,  Mr.  Boase  '  pro- 
ceeds to  say,  "  The  arguments  adduced  by  our  old  historians  in 
proof  of  the  tradition,  refute  themselves.  In  the  first  place,  the  sea 
is  no  shallower  between  the  Land's  End  and  Scilly,  than  at  equal 
distances  from  land,  on  other  parts  of  the  coast ;  and  the  midway 
gulf  or  Wolf- rock,  happens  not  to  be  in  that  channel  at  all.  but  con- 
siderably to  the  south  of  it ;  and  as  to  the  stories  of  fishing  up 
pieces  of  doors  and  windows,  and  seeing  tops  of  buildings,  etc.,  liad 
all  the  buildings,  doors,  and  windows  of  Cornwall,  been  placed 
there,  the  first  tempest  would  have  swept  them  all  awa}^  as  j^ebbles 
before  a  torrent.  The  truth  is,  that  no  such  relics  were  ever  dis- 
covered, or  could  have  remained  for  discovery,  in  that  boisterous 
channel  of  the  Atlantic  Ocean." 

I  p.  29.  «  lb.  p.  30.  3  1527-1593.  *  lb.  p.  29. 

»  T.R.G.S.  Corn.  vol.  ii.  pp.  130,  131.  «  C'arew,  p.  3.  '  Op.  cit.  p.  132. 


TF.  A.  E.  Ussher — Hisiovical  Geology  of  Cornwall.  9 

With  the  above  opinion  I  entirely  agree,  for  the  very  mention  of 
•windows  dredged  up  is  suflficient  to  refute  any  testimony  of  an 
historical  connexion  of  the  Land's  End  with  the  Scilly  Isles  based 
upon  it.  Except  as  fragments  of  wreck,  it  is  impossible  to  conceive 
the  occurrence  of  such  material  in  the  places  specified. 

(Peacock  p.  140.)  The  tradition  of  the  loss  of  area  on  the 
West  of  Land's  End  is  thus  mentioned  by  flarrison  (An  Historical 
Description  of  the  Island  of  Britaine,  by  W.  Harrison,  prefixed  to 
Hollingshed's  Chronicles,  1586,  vol.  i.  lib.  iii.  ch.  10,  p.  397):  "A 
remarkable  corroboration  of  Ptolemy's  positions  of  the  promontories 
Belerium  and  Ocrinum,"'  as  Mr.  JPeacock  thinks,  "It  doth  apeere 
yet  by  good  record,  that  whereas  now  there  is  a  great  distance 
betweene  the  Syllan  Isles  and  point  of  the  Land's  End,  there  was  of 
late  years,  to  speke  of  scarslie  a  biooke  or  drain  of  one  fiidam  water 
betweene  them,  if  so  much,  as  these  evidences  appeereth  and  are 
yet  to  be  seeue  in  the  hands  of  the  lord  and  chiefe  owner  of  those 
Isles." 

Dr.  Paris  and  Mr.  Carne-  considered  that  St.  Just  in  the  Land's 
End  district  might  have  been  meant  by  the  word  Cassiterides,  owing 
to  the  traces  of  tin  in  the  Scilly  Isles  being  insuflScient  to  justify  that 
appellation.  Mr.  Carne,^  speaking  of  Piper's  Hole,  in  Tresco  Island, 
as  a  supposed  adit  of  the  ancient  tin  works,  objected  that  as  it  is 
above  high- water,  it  is  just  such  a  site  as  would  be  selected  now. 
He  further  considers  that,  if  any  mines  had  ever  been  productive  in 
the  Scilly  Isles,  some  traces  of  diluvial  tin  ore  would  even  now  be 
!  found  from  time  to  time  in  the  low-lying  tracts  in  St.  Mary's,  and  on 
i    the  south-eastern  side  of  Tresco. 

Mr.  Peacock*  quotes  Diodorus  Siculus  as  follows: — "Far  beyond 
i  Lusitania  (Portugal)  ver^^  much  tin  is  dug  out  of  the  islands  in  the 
1  ocean  nearest  to  Iberia  (Spain),  Avhich  from  the  tin  are  named 
!    Cassiterides." 

j  D.  P.  Alexandrinus,  who  flourished  in  the  time  of  Augustus,  says 
I  in  his  Geography,  line  599,  etc.  :  "  But  beyond  the  Sacred  Promontory 
i  (Cape  St.  Vincent),  which  they  affirm  is  the  extremity  of  Europe,  in 
the  islands  Hesperides,  where  the  source  of  tin  is,  the  rich  children 
of  the  illustrious  Iberi  dwell."  Mr,  Peacock  thinks  that  the  Scilly 
I  Isles  are  liere  alluded  to  under  the  name  Hesperides. 
,  Strabo  has  told  us  that  Publius  Crassus  saw  that  the  metals  were 
J  dug  out  at  a  little  depth  in  the  Cassiterides  (book  ii.  cap.  v.  §  15)  ; 
•    this  was  about  57  B.C. 

Strabo  further  describes  the  Cassiterides  as  "islands in  the  high 
seas  just  Under  the  same  latitude  as  Britain,  northward  and  opposite 
to  the  Artabri."  ^ 

^  Peacock,  p.  109. 

2  Mr.   Carne   (T  K.G.S.  Corn.  vol.  ii.  p.  354)   says,  "It  is  exceedingly  probable 
that  the  western  extremity  of  England,  of  which  St.  Just  forms  a  prominent  part, 
constituted  the  principal  portion  of  what  was  formerly  known  under  the  name  of  the 
Cassiterides." 
,       *  T.R.G.S.  Corn.  vol.  vii.  p.  153,  «  Peacock,  p,  106, 

*  Peacock,  p.  107. 


10          W.  A.  E.  Ussher — Historical  Geology  of  Cornwall. 


Part  4, —  St.  MiclmeVs  Mount. 

The  best  description  of  St.  Michael's  Mount,  as  it  now  exists,  that 
I  can  find,  is  by  Mr.  Pengellj',^  as  follows:  "The  Mount  is  an 
isolated  mass  of  granite  measuring  about  five  furlongs  in  perimeter 
at  its  base.  At  high-water  it  plunges  abruptly  into  the  sea,  except 
on  the  northern  or  landward  side,  where  the  granite  comes  in  contact 
with  the  slate,  into  which  it  sends  veins  and  dykes,  as  may  be  well 
seen  on  each  side  of  the  harbour.  Here  there  is  a  small  plaia 
occu])ied  by  a  village,  adjacent  to  which  is  the  harbour,  built  in 
172<)-7,  and,  as  Mr.  Johns,  the  harbour-master,  has  been  good  enough 
to  write  me,  capable  of  receiving  ships  of  500  tons  burthen."  Its 
situation  is  described  as  follows  :  "The  distance  between  the  nearest 
point  of  jMarazion  Cliflf  atid  spring-tide  high-water  mark  on  the 
Mount  is  1680  feet.  A  tidal  isthmus  (Hogus)  of  highly  inclined 
Devonian  slate  and  associated  rocks,  in  most  cases  covered  with  a 
thin  layer  of  gravel  or  sand,  is  at  spring-tide  high-water,  in  still 
weather,  12  feet  below  ;  and  at  low- water  6  feet  above  the  sea-level. 
This  ridge  is  dry  in  fine  weather  from  four  to  five  hours  every  tide, 
but  occasionally  daring  storms  and  neap  tides  it  is  not  passable  for  two 
or  three  days." 

"  St.  Michael's  Mount-  was  named  in  Cornish,  as  Carew  informs  us 
'  Caraclowse  in  Cowse,  in  English,  the  hoare  rock  in  tlie  wood : 
which  now  is  at  every  flood  encompassed  by  the  sea,  and  yet  at 
some  low  ebbs,   roots    of  mighty  trees    are  descried  in  the    sands 

about  it.' Florence  of  Worcester  expressly  asserts  that  it 

was  formerly  five  or  six  miles  from  the  sea  and  enclosed  with  a  very 
thick  wood  ;  and  therefore  called  in  British,  Carreg  lug  en  Kug, 
'  Le  Hore  Eok  in  the  wodd.'  " 

The  above  is  said  to  have  been  corrected  by  Florence  of  Worcester 
in  a  letter  to  "William  of  Worcester,  1478.^ 

Mr.  Peacock  *  thinks  that  we  need  not  go  back  further  than  the 
time  of  the  Domesday  Book  for  the  origin  of  the  Cornish  name  of  l 
St.  Michael's  Mount,  "Carreg  coedh  yn  clos,"  i.e.  "  Rock  of  the  wood 
in  the  enclosure,"  as  William  Camden  (1550-1623)  "proves  that 
the  Cornish  language  had  not  become  quite  extinct  even  so  lately  as 
bis  time." 

"  Dr.  Gibson,^  the  editor  of  Camden's  Britannia,  says  that  St. 
Michael's  Mount  is  called  Carreg  Cowse  in  Clowse.  Carreg  is,  doubt- 
less, the  origin  of  the  English  word  crag;  and  cowse  is  said  to  mean 
cana,  white ;  and  clowse  obviously  means  a  close  or  enclosure." 

"  Mr.  IMetivier  says  that  St.  Michael's  Mount  was  '  Carreg  Coed 
yn  Clos,'  rock  of  the  wood  in  the  enclosure." 

Mr.  Peacock^  says  that  "  the  earliest  period  at  which  the  Saxon 

'  Journ.  Roy.  Inst.  Corn,  for  1873,  p.  12. 

»  T.  E.  G.  S.  Corn.,  vol.  ii   p.  134. 

3  Pongelly  on  Submerged  Forests  in  Torbav-  *  Peacock,  p.  110. 

»  Ibid.  p.  89.  ■  •  p.  111. 


TF.  A.  E.  Ussher — Jlistorical  Geology  of  Cormcall.         11 

name  Mychel  Stop,  or  Michael's  Step,  could  have  been  given  to  the 
Mount,  was  after  the  landing  of  Hengist  and  Horsa  in  449." 

Tiie  Mount  received  its  present  name  in  1085,  from  the  Monastery 
of  St.  Michael,  of  which  it  then  became  an  appanage ;  before  that 
time  it  was  called  Dinsol.^ 

"  In  Milner's  Gallery  of  Nature,  p.  387,  it  is  stated  that  in  the 
time  of  Edward  the  Confessor,  1044,  the  rock  of  St.  Michael's 
Mount  was  the  site  of  a  monastery  described  as  being  near  the  sea, 
'juxta  mare'  (interpreted  by  Dr.  Barham,  'by  the  sea').  " 

"  The  ancient  designation,"  says  Mr.  Pengelly,  "betokens  a  change 
in  tlie  geography  of  the  district — a  change,  not  only  within  the  human 
period,  but  since  Cornwall  was  occupied  by  a  people  who  spoke  the 
language  which  was  tardily  supi^lanted  by  the  Anglo-Saxon." 

Mr.  Pengelly  refers  the  name  "  Hogus,"  now  applied  to  the  rocky 
ledge  between  Marazion  and  the  Mount,  to  an  old  Scandinavian 
derivation,  meaning  "a  rock  in  or  near  a  wood  adjacent  to  water, 
and  used  for  sacrificial  purposes." 

Mr.  Peacock'-  takes  exception  to  this  determination  on  the  ground 

that   Hogus   (in  Guernsey  hougue,  French  hogue,  neo-Latin  hoga) 

sometimes  denotes  a  quarriable  knoll,  of  which  he  gives  examples. 

;    From  this  Mr.  Peacock  infers  that  the  terra  Hogus  only  carries  us 

j    to  the  middle  ages,  and  not  to  the  time  of  Diodorus. 

Mr.  Peacock^  cpiotes  Diodorus  Siculus  (about  44  B.C.)  as  follows: 

"They    who    inhabit    the    promontory   Belerium    are    exceedingly 

hospitable,  and  on  account  of  the  merchants  being  their  guests  are 

civilized  by  custom  in  their  mode  of  life.     They  procure  the  tin  by 

;    ingeniously  working  the  earth  producing  it,  which,  being  rocky,  has 

earthy  veins,  in  which  working  a  passage  and  melting  (the  ore)  they 

,    extract  [the  tin].    Forging  it  into  masses  like  Astragals,  they  carry  it 

I    into  an  Island  situate  before   Britain,  called  Ictis.     For  the  middle 

i    space  being  dried  by  the  ebb  they  carry  the  tin  into  this  (island)  in 

I   abundance   in  carts.     (But  a  certain  peculiar  thing  happens  con- 

i    cerning   the  neighbouring  islands    lying   in    the  middle    {fiera^u) 

between   Europe   and    Britain,  for   at  full    sea   they  appear  to  be 

islands,  but  by  the  reciprocation  of  the  ebb  of  the  sea,  and  a  large 

space  being  dried,  they  appear  peninsulas.)     Hence  the  merchants 

buy  [the  tin]  from  the  inhabitants  and  export  it  into  Gaul." 

Taking  fiera^u  to  mean  "  in  the  middle,"  Mr.  Peacock  considers 
that  the  Northern  Channel  Islands  were  alluded  to  in  the  above 
passages,  being  of  opinion  that  the  Northern  Channel  Islands  were 
then  only  insulated  at  high-water,  and  that  they  are  called  neigh- 
bouring islands  to  distinguish  them  from  the  more  remote  islands  in 
■  the  Bay  of  Biscay. 

Mr.  Pengelly  *  observes  that,  according  to  Leland,  St.  Michael's 
Mount  in  1533  was  no  larger  than  at  present ;  that  William  of 
Worcester's  estimation  of  its  distance  from  the  mainland  differs  but 
little  from  its  present  site  :  that  "  Bishop  Lacy's  encouragement  to 
the  Faithful  in  1425  to  complete  a  causeway  between  Marazion  and 
>  Ibid.  p.  112.  »  Peacock,  p.  107. 

*  Peacock,  p.  86.  ♦  Journ.  Eoy.  Inst.  Corn,  for  1873,  p.  181. 


12  W.  A.  E.  Ussher — Historical  Geology  of  Conucall. 

the  Mount,  for  the  protection  of  life  and  shipping,  denotes  that  the 
exposure  was  as  great  as  in  our  day  ;  and  as  the  Confessor's  Charter 
in  1044  describes  the  Mount  as  '  juxta  mare,'  '  next  or  by  the  sea,  it 
may  be  safely  concluded  tliat  the  insulation  of  the  Mount  had  taken 
place  more  than  eight  centuries  ago." 

After  a  passing  allusion  to  other  competitors  for  the  Ictis  of 
Diodorus,  he  saj^s,  "  It  is  perhaps  worthy  of  remark,  that  those  who 
have  studied  the  Geology  of  Cornwall,  espoused  the  cause  of  the 
Mount;  while  those  who  fail  to  do  so,  appear  to  have  come  to  the 
question  with  their  minds  imbued  with  a  belief  in  William  of 
Worcester's  statement,  that  there  were  140  parish  churches  sub- 
merged between  the  Mount  and  Scilly,  and  accordingly  hold  that 
the  submergence  took  place  not  only  since  the  time  of  Diodorus,  but 
since  the  introduction  of  the  parochial  system  into  Cornwall." 

Mr.  Pengelly  quotes  Sir  George  Cornewall  Lewis  (An  Historical 
Survey  of  the  Astronomy  of  the  Ancients)  as  follows  :  "  Timaeus 
mentions  an  island  of  Mictis  within  six  days'  sail  of  Britain  which 
produced  tin,  and  to  which  the  natives  of  Britain  sailed  in  coracles." 
He  regarded  Mictis  and  Ictis  as  variations  of  Vectis. 

From  Mr.  Pengelly 's  statement  that  the  Mount  1900  years  ago 
possessed  a  harbour,  Mr.  Peacock  dissents  on  the  ground  that  "  if 
the  coast  had  remained  unaltered  ever  since  Diodorus's  time,  the 
Eoman  tin-transporting  ships  need  not  by  any  means  have  been 
confined  to  St.  Michael's  Mount  as  a  harbour,  because,  as  the  Eev. 
W.  Borlase-  well  observes,  Guavas  Lake  is  the  principal  anclioring' 
place."  Whence  he  considers  that  the  chief  export  of  tin  could  not 
have  taken  place  from  St.  Michael's  Mount,  and  does  not  favour  the 
belief  in  its  identification  as  the  Ictis  of  Diodorus.  He  says  further:* 
"The  ancient  block  of  tin  which  was  dredged  up  about  1823  in 
Falmouth  Harbour  (Lyell's  Princii)les  of  Geology,  18fi7,  p.  451),  if 
we  suppose  it  to  have  been  dropped  during  its  transit  to  tlie  Isle  of 
Ictis,  would  seem  to  place  Ictis  opposite  Falmouth  harbour,  and 
therefore  twenty  miles  east  of  St.  Michael's  ]\Iount." 

Mr.  Pengelly,  in  a  lecture  at  the  Royal  Institution.^  says,  "The 
Mount  is  by  no  means  a  solitary  rock  of  its  kind.  Within  seventy 
miles  east  of  it  there  are  certainly  four  that  actually  are  or  probably 
were,  within  the  last  1900  years,  precisely  similar  though  slightly 
larger  islands — Looe  Island,  St.  Nicholas  Island,  the  Mewstone,  and 
Borough  Island." 

Mr.  Peacock  cherishes  the  idea  that  the  Mounts  Bay  forest  was 
submerged  in  the  historic  period,  and  is  sufficient  confirmation  of  the 
"tradition  of  these  parts  that  St.  Jlichael's  Mount,  now  enclosed  half 
a  mile  with  the  sea,  when  the  tide  is  in,  stood  formerly  in  a  wood." 

He  quotes  the  following  note  from  Carew  (1602):*  "Tradition 
tells  us  that  in  former  ages  the  Mount  was  part  of  the  insular 
continent  in  Britain,  and  disjoined  from  it  by  an  inundation  or  en- 
croachment of  the  sea,  some  earthquake  or  terrestrial  concussion." 

'  "  Sanctum  Michaelum  qui  est  juxta  mare." 

=*  Phil.  Trans,  vol.  48.  '  Peacock,  p.  118. 

*  Quoted  by  Peacock,  p.  139.  *  p.  140. 


W.  A.  E.  Ussher — Historical  Geology  of  Cornicall.         13 

"If,"  says  Mr.  Peacock,^  "the  storm  of  1099  and  Dr.  Borlase's 
submersiou-  in  the  nintli  century  be  true,  St.  Michael's  Mount 
cannot  have  been  the  ancient  isle  of  Ictis,  because  must  we  not 
suppose  that  the  Mount  only  became  an  island  at  one  of  these 
submersions."  Mr.  Peacock  strengthens  his  position  by  the  following 
quotation^  from  page  2  of  the  Domesday  Book:  "The  land  of 
Michael  .  .  .  there  are  two  hides  which  never  paid  the  Danish  tax 
(nunquam  geldaverunt).     The  land  is  eight  caracutes." 

The  hide  is  generally  supposed  to  be  equal  to  120  acres.*  Sir.  H. 
Ellis  says  that  the  measure  of  a  hide  varied  in  different  places  at 
different  times.  "  The  caracute  was  as  much  arable  land  as  could  be 
managed  with  one  plough  and  the  beasts  belonging  thereto  in  a  year; 
having  meadow,  pasture,  and  houses  for  the  householders  and  cattle 
belonging  to  it." 

Tailing  the  smallest  estimate  of  a  "hide"  from  the  five  different 
measures  of  it  in  the  reigns  of  Richard  I.,  Edward  I.,  and  Edward  XL, 
which  vary  from  60  to  180  acies,  Mr.  Peacock  says  that  eight 
caracutes  would  have  amounted  to  490  acres,  whilst''  the  present 
dimensions  of  the  Mount,  measured  from  the  Ordnance  Map,  "are 
found  to  average  22  X  14  chains;  the  area  therefore  is  30"8  acres;  * 
and  it  is  quite  clear  that,  so  far  from  tliere  being  eight  caracutes  of 
arable  land,  there  can  hardly  be  a  single  acre  capable  of  being 
ploughed,  because  the  ground  is  too  steep  and  rocky." 

Mr.  Peacock '  believes  that  at  the  date  of  this  description  in  the 
Domesday  Book  (in  the  year  1086),  St.  IMichael's  Mount  was  not  an 
island,  for  the  following  reasons  :  Firstly,  because  neither  the 
Domesday  Book  nor  the  Saxon  name  Michael  Stop  give  any  reason 
for  such  a  conclusion.  Secondly,  because  it  is  the  custom  in  the 
Domesday  Book,  "  when  a  place  is  an  island,  to  call  it  so."  Of  this  he 
gives  examples.  Thirdly,  on  account  of  its  then  containing  at  least 
eiglit  times  as  much  land  as  at  present. 

Of  the  several  remaining  competitors  for  the  Ictis  of  Diodorus,  Mr. 
Peacock  disposes  as  follows  : — 

As  the  Scilly  Isles  do  not  lie  between  Europe  and  Britain,  and  as 
\  there  is  a  43-fathom  sounding  between  them  and  the  Land's  End, 
'    none  of  them  would  answer  to  the  description  of  Ictis. 

As  to  the  Isle  of  Portland  or  the  Isle  of  Wight,  so  accurate  an 

■  observer  as  Diodorus  would  not  have  failed  in  distinguishing  their 
position  definitely  as  "  near  the  south  coast  of  Britain,  nor  are  there 

;  any  grounds  for  the  supposition  that  the  relations  of  either  locality 

\  to  the  mainland  were  different  in  Diodorus's  time  from  the  present." 
[       With  respect  to  the  claims  of  Mont  St.  Michel,  he  considers  that  the 

i  space  between  it  and  the  Continent  was  the  Forest  of  Scisy  and  not 

■  sea  until  seven  centuries  and  a  half  after  Diodorus's  time. 

1  Peacock,  p.  88. 

'    _    *  Dr.  Borlase  was  inclined  to  refer  the  submersion  of  St.  Michael's  Wood  to  the 

i    inundation  of  the  year  830,  mentioned  in  Irish  Annals.  Mr.  Whitaker  ascribed  it  to 

i    that  mentioned  by  the  Saxon  Chronicle  and  Florence  of  Worcester  as  occurring  in 
1099.      Vide  T.  R.  G.  S.  Corn.,  vol.  ii.  p.  139. 

3  Peacock,  p.  137.  *  lb.  p.  113. 

'  lb.  p.  135.                                   «Ib.  p.  lit.  "  lb.  pp.  112,  113. 


14  W.  A.  E.  JJssher — Historical  Geology  of  Cornwall. 

As  alternatives,  Mr.  Peacock  proposes  the  Wolf  Eock  (which  would 
be  opjjosite  Britain  if  a  westerly  and  north-westerly  extension  of 
the  Cornish  coast  be  conceded)  ;  the  Seven  Stones;  or  some  island 
now  totally  lost.  He  considers,  however,  that  the  identification  of 
Ictis  is  "  both  impossible  and  unimportant." 

Mr.  Claypole '  gives  an  estimate  of  the  uniform  rate  of  depression 
of  Mounts  Bay  on  assuming  the  identity  of  St.  Michael's  Mount 
with  the  Ictis  of  Diodorus  and  the  Ocrinum  of  Ptolemy.  He  says : 
"  It  must  then  have  been  an  island  as  now  at  high-water  onl)'.  In. 
the  time  of  Diodorus  the  isthmus  must  have  been  below  high-water 
mark.  So  depression  must  be  restricted  to  limits  allowing  the 
isthmus  to  have  been  below  the  upper  limit  of  2U-foot  tide,  1800 
years  ago,  and  above  its  lower  limit  now :  so  that  it  would  not  have 
exceeded  6  feet,  therefore  the  rate  of  depression  would  be  4:  inches 
per  century,  which  would  be  G  feet  in  12,600  years." 

Mr.  Pengelly,^  commenting  on  the  evidence  furnished  by  the 
caverns  of  Devon,  gives  the  following  general  note,  whicli  may  not 
be  out  of  place  here  :  ''In  order  to  obtain  the  whole,  we  must  add 
to  this  part  the  time  represented  by  the  lodgement  of  the  blue 
Forest  Clay  of  Devon  or  the  tin  ground  of  Cornwall,  to  this  again 
must  be  added  the  period  in  which  the  forests  grew  ;  to  this  a  further 
addition  must  be  made  of  the  time  during  which  the  entire  country 
was  carried  down  at  least  70  feet  vertically  by  a  subsidence  so  slow 
and  tranquil  and  uniform  that  it  nowhere  throughout  the  ai-ea  of 
Western  Eurojie  and  the  British  Islands  disturbed  the  horizontality 
of  the  old  forest  soil ;  and  finally  we  must  also  add  the  time  which 
has  elapsed  since — a  time  which  of  itself,  thanks  to  the  description  of 
St.  Michael's  Mount  by  Diodorus  Siculus,  we  know  certainly  ex- 
ceeded 2000  years,  and  which  the  volume  of  the  stratified  deposits 
overlying  the  forests,  as  well  as  the  amplitude  of  the  existing  fore- 
shore, warrants  our  believing  exceeded  it  by  a  very  large  amount." 

Conclusion. — If  the  word  Cassiterides,  in  the  writings  of  Strabo, 
Posidonius,  and  Diodorus,  refers  to  the  Scilly  Isles,  and  if  they  have    T 
also  been  mentioned  by  Dionysius  Alexandrinus  under  the  name  of 
Hesperides,  the   quotations  from   these   authors  would   imply  the 
following  consequences. 

First, — That  tin  must  have  been  obtained  in  the  Scilly  Isles  as    , 
they  then  existed. 

Secondly, — Tiiat,  as  no  productive  tin  veins  or  signs  of  old  work- 
ings are  found  on  these  islands,  such  workings  must  have  been 
carried  on  in  districts  now  submerged,  at  a  time  when  the  number 
of  the  islands  (allowing  a  considerable  margin  on  the  score  of 
insignificance  in  Strabo's  account)  was  much  less  than  at  present, 
and  when  the  flats  between  the  islands  of  Tresco,  St.  Mary,  and  St. 
Martin  (as  may  reasonably  be  inferred  from  Dr.  Borlase's  descrip- 
tion), were  dry  land  at  high-water  and  above  the  level  of  spring- 
tides. 

Thirdly, — That  the  Channel  Islands  were  not  insulated  in  Diodorus' 

'  Proc.  Brist.  IS'at.  Soc.  1870,  vol.  v.  p.  35. 
^  Journ.  Iloval  Instit.  Corn,  for  1873. 


W.  A.  E.  Ussher — Historical  Geology  of  Cornioall.         15 

time ;  for,  if  they  were,  he  would  hardly  have  alluded  to  the  Scilly 
Isles  as  nearest  to  Iberia.  This  accords  with  Mr.  Peacock's  views  as 
to  their  more  recent  insulation. 

Fourthly, — From  Alexandrinus'  account,  must  we  not  supj^ose 
that  the  inhabitants  of  the  islands  were  a  colony  from  Spain  in  his 
time,  and  either  supplanted  the  original  inhabitants  alluded  to  by 
Dr.  Borlase,  or  were  themselves  succeeded  by  a  British  race, 
addicted  to  Druidic  rites  ? 

Notwithstanding,  I  am  inclined  to  think  tliat  the  word  "  Cassi- 
terides  "  was  indiscriminately  used  for  the  Scill}^  Isles  and  Land's 
End  District,'  owing  to  the  imperfect  navigation  of  those  early  days 
of  naval  commerce. 

Diodorus's  description  of  the  inhabitants  and  mineral  wealth  of 
Belerium  would  apply  rather  to  a  district  of  tliat  name  than  to  an 
individual  promontory,  and  it  does  not  seem  improbable  that  the 
name  of  one  of  its  most  important  headlands  should  be  indiscrimi- 
nately applied  to  the  whole  stanniferous  district  of  the  Land's  End. 
If,  as  Mr.  Peacock  supposes,  the  Northern  Channel  Islands  are 
spoken  of  by  Diodorus  as  neighbouring  islands  with  reference  to 
Ictis,  one  can  scarcely  agree  with  him  in  disposing  of  the  claims  of 
the  Isle  of  Wight  to  the  appellation  of  Ictis  on  the  ground  of  the 
accuracy  of  that  historian's  descriptions.  If  the  name  Vectis^  applied 
exclusively  to  the  Isle  of  Wight,  Pliny's  mention  of  it  as  lying 
between  Ireland  and  Britain  would  prevent  one  from  putting  too 
much  faith  in  the  latitudes  and  longitudes  of  ancient  geographers. 
(Vide  Note  B.) 

To  revert  to  more  recent  records.  As  the  description  of  St. 
Michael's  Mount  in  the  Domesday  Book  is  so  indefinite,  and,  from 
the  nature  of  the  record,  rather  applicable  to  the  lands  belonging 
thereto  than  to  the  geographical  position  of  the  Mount  itself,  there 
appears  to  be  little  reason  why  the  eight  caracutes  mentioned  in  the 
passage  should  not  be  regarded  as  arable  lands  on  the  adjacent 
mainland  belonging  to  the  monastery. 

The  submergence  of  the  Mounts  Bay  forest  seems  to  have 
occurred  considerably  anterior  to  any  inundation  on  record,  for  the 
following  reasons. 

First, — Mr.  Carne^  mentions  the  extension  of  the  old  forest  ground 
seaward,  traced  to  a  depth  of  from  twenty  to  thirty  feet  below  spring- 
tide level. 

Secondly, — There  is  every  reason  to  conclude,  with  Mr.  Carne,  that 
the  forest  bed  met  with  in  a  pit  at  Huel  Darlington  mine,  under 
12  feet  of  marine  sediuient,  four  feet  of  peat,  and  eight  feet  of  river 
wash,  is  continuous  with  the  forest  bed  on  the  beach. 

Thirdly, — Whilst  the  entombment  of  the  forests  in  marine  sedi- 
ments indicates  subsiding  movements,  the  peat  and  overlying  gravel  in 

1  T.  E.  G.  S.  Corn.  vol.  vii.  p.  153. 

=*  (Peacock,  p.  183.)  Pliny,  Nat.  Hist.  lib.  iv.  §  30:  "  Sunt  antera  xl  Orcades 
modicis  inter  se  discretse  spatiis.  Septem  Acmodae,  et  xxx  Hebrides ;  et  inter 
Hiberniam  ac  Britanniara,  Mona,  Monapia,  Ricina,  Vectis,"  etc. 

»  T.  R.  G.  S.  Corn.  vol.  vi.  p.  230,  etc. 


16  IV.  A.  E.  Ussher — Historical  Geology  of  Cormcall. 

Marazion  Marsh,  and  the  present  positions  of  rock  platforms  slightly- 
higher  than  spring-tide  at  high-water,  and  of  estuarine  deposits, 
seem  to  point  to  a  slight  subsequent  elevation,  not  yet  counteracted. 
The  changes  which  took  place  after  the  submersion  of  the  old  forest 
ground  can  hardly  have  been  comprised  in  eight  centuries,  and  were 
more  probably  operating  during  a  period  of  more  than  2000  years. 
A  belief  in  the  pre-historic  '  submergence  of  the  Mounts  Bny  forest 
is  b}'  no  means  contrary  to  the  identification  of  St.  Michael's  Mount 
"with  the  Ictis  of  Diodorus  ;  for,  although  the  land  ma}'  have  been 
at  a  slightly  lower  level  in  the  time  of  Diodorus  than  at  present, 
the  rajiid  disappearance  of  thirty-six  acres  of  pasturage  from  the 
West  Green  sand-banks^  since  Cliarles  tlie  Second's  time,  mentioned 
by  Dr.  Boase  (T.Ii.G.S.  Corn.  vol.  iii.  p.  131),  leaves  one  free  to  infer 
that  prior  to  that  time  the  bank  was  of  still  greater  extent,  so  that 
its  eastward  portion  may  have  facilitated  the  passage  to  the  Mount 
b}'  affording  a  ridge  or  causeway  of  sand  covering  the  rocky  isthmus 
and  passable  in  most  conditions  of  the  tides.  Tlie  Wolf  Rock  and 
the  Seven  Stones  can  scarcely  be  regarded  as  possible  competitors  for 
the  Ictis  of  Diodorus;  their  admission  wouhl  entail  a  subsidence  of 
at  least  200  feet  within  2000  years,  as  the  former  is  seven  miles  to 
the  south-west  of  Guethenbras  Point  (Laml's  End  district),  with. 
intervening  depths  of  from  twenty-one  to  thirt3'-eight  fathoms  ;  and 
the  latter  are  fourteen  miles  west  from  the  Land's  End,  with  depths 
of  thirty-two  to  forty  fathoms  between  them  and  the  Longsliips. 
St.  Michael's  Mount  appears  better  to  accord  with  the  description  of 
Diodorus  than  anj'  other  island  on  the  Cornish  coast,  on  account  of, 
firstly,  its  vicinity  to  tin-producing  districts  ;  secondl}'.  the  facility  i 
with  which  carts  laden  with  the  ore  could  have  reached  it,  either  i 
on  the  supposition  of  an  elevation  of  a  few  feet,  or  allowing  the 
extension  of  the  sand-bank  from  the  mainland  or  the  existence  of  a 
sand  spit  concealing  the  isthmus. 

APPENDIX. 

Note  A. — A  rock  near  the  Land's  End  bears  the  name  of  "the  Armed  Knight." 
Thouo-h  this  appelLation  may  have  been  bestowed  on  it  through  a  fancied  resemblance 
in  outline,  the  existence  of  the  tradition  respecting  Trevelyan's  adventure  appears  to 
furnish  a  more  likely  reason  for  the  name. 

Note  B.— In  Speed's  Map  of  Cornwall,  1610,  no  dependence  can  be  placed  upon  the 
latitudes,  as  may  be  seen  by  placing  a  tracing  of  a  reduced  Ordnance  Map  of  the 
same  scale  (about  1  inch  to  4  miles)  over  it,  when  the  Land's  End  district  will  be 
found  to  occupy  entirely  different  positions  scarcely  overlapping  in  any  place,  and 
the  shape  of  the  Lizard  district  to  be  quite  dissimilar. 

Another  map  without  date,  but  probably  as  old  as  Speed's,  was  shown  to  me  by 
Mr.  Parfitt,  of  the  Devon  and  Exeter  Literary  Institute  ;  the  same  discrepancies  were 
visible  in  it. 

Now  when  we  find  discrepancies  of  latitude  equal  to  10',  and  the  shapes  of  pro- 
montories entirely  misrepresented  in  maps  of  their  own  country  produced  by 
geographers  300  years  ago,  how  can  we  expect  to  find  even  as  great  accuracy  in  the 
geographical  descriptions  of  Roman  or  Greek  historians,  more  especially  when 
relating  to  coasts  with  which  they  must  at  best  have  been  very  slightly  acquainted  ? 
1  As  far  as  Britain  is  concerned. 
'  The  banks  are  now  only  two  or  three  acres  in  extent. 

ERRATA.-p.  7,  line  31,  for  "  10  to  20"  read  "  10  to  12  ;"  p.  8,  line  12,  for 
"  400,"  read  "  440." 


17 


PART    II. 

FOST-TEETI^ETT    GEOLOaY    OF    COKNTV^LX,. 

THE  materials  for  a  classification  of  the  later  Pleistocene  deposits 
of  Cornwall  are  so  voliiminous  that  it  was  found  impossible  to 
embody  them  in  a  single  paper.  Having  elsewhere  attempted  a 
general  classification  with  such  notices  of  the  deposits  as  seemed 
necessary  to  sliow  the  grounds  whereon  it  was  based,  I  purpose 
in  tlie  following  paper  to  complete  the  notices  of  deposits.  As  an 
apology  for  the  amount  of  compilation  thus  rendered  necessary,  I 
must  plead  the  object  of  the  papers,  viz.  to  place  in  one  view  all 
that  has  been  written  on  the  subject,  as  references  alone  would 
entail  more  time  and  trouble  in  looking  up  than  many  readers  would 
be  disposed  to  concede. 

The  paper  is  divided  into  the  following  sections  : — 
1.  Oldest  superficial  deposits;    2.  (o)  Boulder  Gravels,  (fc)  Raised 
Beaches,  and   (c)   "  Head."     3.  Submei'ged  Forests  and  Stream-Tin 
Gravels.     4.  Eecent  Marine  and  Blown  Sands. 

1.  Oldest  Superficial  Deposits. 

From  their  isolated  positions,  and  evident  relations  to  an  entirely 
different  surface  configuration,  the  gravels  of  Crousa  Down  and 
Crowan,  and  the  sands  and  clays  of  St.  Agnes,  must  be  regarded  as 
the  earliest  traces  of  superficial  deposits  as  yet  observed  in  Cornwall. 

Gravels  of  Crousa  Down  and  Croican. — On  Crousa  Downs,  Lizard 
District,  a  patch  of  rounded  and  subangular  quartz  gravel  "  occupies 
an  area  of  about  half  a  square  mile  at  a  height  of  about  360  feet 
above  the  sea"  (Report  on  Geol.  Corn,  and  Dev.  p.  396). 

The  Rev.  E.  Budge  (Trans.  R.  G.  S.  Corn.  vol.  vi.  pp.  1  and  91) 
describes  the  deposits,  generally,  as  extended  layers  of  fine  yellow 
gravel,  with  a  quantity  of  quartz  pebbles,  exposed  in  pits  10  to  12 
feet  deep  in  places,  near  the  road  leading  to  Coverack.  The 
character  of  the  sections  is  given  thus — Black  peaty  soil  containing 
small  angular  quartz  stones  about  6  inches  thick,  upon  layers  of  fine 
and  very  coarse  gravel  alternating  in  no  very  determinate  order, 
containing  quartz  pebbles  of  very  irregular  form,  some  as  large  as  a 
man's  head,  but  for  the  most  part  not  exceeding  2  to  3  inches  in 
length.     The  Crousa  Down  gravel  rests  on  Diallage  rocks. 

A  similar  occurrence  was  noticed  by  Mr.  Tyack  (62nd  Ann.  R.  Geol. 
Soc.  Corn.  p.  176,  etc.)  at  Blue  Pool  in  Crowan.  The  pebbles  covered 
an  area  of  800  yards  from  north  to  south,  and  oOO  from  E.  to  W. 


18        rr.  A.  E.  Unshcr—Post-Toiiary  Geology  of  Cormcall. 

Tlioy  are  sfattei-od  OA'cr  tlip  siirfuce,  are  well  worn,  and  vary  in  size 
from  ial■,^■^■  IiouIiIits  to  tlie  dinicnsions  of  liazfl  nms.  'J'lie  <;iavel  is 
4UU  fet-t  aliove  I  lie  sea,  it  rests  on  jellow  clay.  As  at  Cronsa  Down 
the  quartz  is  such  as  would  be  liirnished  by  veins  in  the  Killas,  the 
])ebliles  of  scliorl  bi'ini;  very  few,  and  the  occasional  granite  fraj;- 
nients  angnlar ;  yet  the  Killas  districts  near  Crowan  are  at  a  much 
lower  elevation  than  the  granite  on  which  the  pebbles  are  found. 

'I'liese  quartz  gravels  apfiear  to  have  been  derived  from  quartz- 
iferons  Killas,  either  by  ilirecl  transport  of  aqueous  agencies  suffi- 
ciently protracted  in  their  operation  to  allow  of  the  connuinution  of 
the  slaty  matter,  or  indirectly  by  the  disintegration  and  redepositioa 
of  a  quartz  conglomerate  rock  of  Palaeozoic  age.  Eel'erring  to  the 
derivation  of  the  Crousa  Down  Gravel,  the  Eev.  E.  Budge  illustrates 
the  prevalence  of  quartz  veins  in  the  Killas  to  the  north  by  citing 
the  occurrence  of  masses  of  quartz  in  the  slates  near  Nare  Point, 
whence  they  can  be  traced  for  some  miles  along  the  line  of  strike; 
and  of  a  quartz  vein.  10  feet  wide  on  the  south-west  of  Game,  in  St. 
Anthony  parish. 

Between  the  Loo  Pool  and  Marazion,  on  the  top  of  the  cliffs,  near 
Trewavas  Head,  small  flint  and  quartz  j^ebbles  occur  in  the  soil,  and 
do  not  appear  to  extend  more  than  a  few  paces  inland.  As  tlieir 
height  above  the  sea  and  the  adjacent  configuration  preclude  the 
possibilit}'  of  their  being  the  relics  of  a  raised  beach,  I  am  forced  to 
conclude  that  the}'  are  either  traces  of  gravels  somewhat  similarly 
situated  to  those  of  Cronsa  Down  and  Crowan,  or  that  during 
exceptionally  severe  gales  some  of  the  smaller  pebbles  of  the  beach 
below  had  been  from  time  to  time  carried  upward  in  the  spray  and 
landed  on  the  top  of  the  clift". 

Deposits  of  St.  Agues. —  (Report,  etc.,  p.  25S).  De  la  Beche  was^ 
disposed  to  regard  the  sands  and  clays  which  nearly  encircle  th« 
higher  parts  of  St.  Agnes  Beacon  as  '"the  remnant  of  some  supr* 
cretaceous  deposit."  "  'J'hey  occur  at  an  elevation  of  between  3i)0 
and  400  feet  above  the  level  of  the  sea,  resting  upon  the  slates  of 
the  hill,  and  partly  also  on  a  small  portion  of  the  granite  rock  which 
there  occurs  ;  the  granitic  rock  and  slates  being  traversed  by  several 
tin  lodes."  "This  isolated  deposit  has  not  hitherto  been  found  to 
contain  organic  remains,  with  the  exception  of  some  traces  of  plants 
that  have  the  ajjpearance  of  P'ucoids." 

The  following  sections  are  given  by  De  la  Beche  (Eeport,  p.  2o9); 
Hawkins  (Trans,  liuy.  Geol.  Soc.  Corn.,  vol.  iv.  p.  18;j,  etc.)  ;  Hen- 
•wood  {pp.  cit.  vol.  V.) ;  respectively — on  the  North-east  of  the  Beacon. 
Numbers  affixed  for  reference  : 

(1)    Head  of  rubble  from  bill  above  or  Cobb 

Yellow  sand     

Brownish  sand  with  numerous  planes  dipping  at  45"  (apparently 

bedding) 

Light-Coloured  mining  clay 

Blue  clay 

Yellow  sand     

Wiiite  sand     

Yellow  sand     

Pebbles  resting  upon  an  uneven  surface  of  slate— thickness  variable 


3ft. 

Oin. 

2it. 

Oin. 

lift. 

Oin. 

2ft. 

Cin. 

9ft. 

Oin. 

4ft. 

Oin. 

4  ft. 

Oin. 

Sft. 

Oin. 

W.  A.  E.  Ussher — Post-Tertiary  Geology  of  Cornwall.       19 

(2)  Near  Trevaunance — 

Yellow  Cobb  with  Killas  rubble       

Fire  clay     2ft.     Oin. 

Clay  and  sand      3ft.     Oin. 

Fine  white  gritty  sand— depth  not  ascertained. 

(3)  Half  a  mile  from  the  Beacon — 

Siu'face  383  feet  above  high  water. 

Clay      2ft.     Oin. 

Yellow  sand,  7  feet  below  the  surface      8ft.     Oin. 

The  overburden  not  mentioned  would  seem  to  be  5  feet  thick. 
The    following  sections  given  by   Messrs.  Kitto  and  Davies  lie 
toward  the  North-east  of  the  Beacon  (Trans.  li.  G.  Soc.  Corn.,  vol.  ix.)  : 

(4)  Near  the  outer  margin  of  the  deposit — 

Head    

Yellow  sand 

Red  sand      

White  sand 

Pebbles  in  sand  not  ffone  throu'rh. 


5ft. 

Oin. 

2ft. 

Oin. 

2  ft. 

Oin. 

4ft. 

Gin. 

6ft. 

Oin. 

3ft. 

Oin. 

12ft. 

Oin. 

2ft. 

Oin. 

Sections  near  the  above  on  N.W.  and  S.W. 

(5)  OnX.W.-Head    

Clay  with  a  few  pebbles    

Sand     

Sandstone     

Sand  with  pebbles  not  gone  through. 

(6)  On  S.W. — Very  sandy  overlmrden,  with  numerous  quartz  pebbles  from  the 

size  of  a  marble  to  that  of  a  walnut,  beneath  wliich  clay  only  is  raised 
varying  from  6  to  12  feet  in  thickness. 

On  the  inner  margin  of  the  deposit  to  the  west  of  the  above, 
"mining  operations  in  1865  exposed  a  cliff  facing  North,  16  feet  in 
heiglit,  anil  15  feet  below  the  surface,"  nearly  perpendicular, 
"smoothed  and  polished"  and  worn  "into  caves  and  hollows."  An 
adit  cut  through  to  the  sand  on  the  other  side  proved  this  to  have 
been  in  all  probability  a  projection  irom  a  main  cliff  face,  whicb  old 
miners  state  to  occur  facing  eastward  for  some  distiuice  to  the  south- 
ward, and  to  be  worn  into  numerous  holhnvs.  The  sand  in  this 
part  of  the  deposit  "  contained  very  large  pebbles  and  boulders  and 
angular"  stones. 

Compare  the  section  given  by  De  la  Beclie  (op.  cit.)  Avith  the  fol- 
lowing by  Hawkins  on  the  North  side  of  the  Beacon  (oj).  cit.),  and 
by  Henwood,  locality  not  specified   (oj).  cit.)  : 

(7)  Yellow  Cobb  with  rubble  of  Killas  stones 2ft.    Gin. 

Brown  sand  with  sedimentary  divisions  dipping  S.  at  45°...     91t.    Oin. 

White  Clay    4in.  to  Sin. 

Brown  and  bluish-giey  clay   (with  a  slight  admixture  of 

carbonaceous  matter)    9ft.orl0ft.    Oin. 

Gritty  sand     6ft.  or  7ft.     Oin. 

(8)  Loose  stones  and  earth,  up  to      6ft.  or  8ft.     Oin. 

Pink,    vellowish,  and  brownish  sand,   in  layers   dipping 

southward 2ft.  to  10ft.    Oin. 

(In  the  lower  portions  small  ferruginous  crusts  and  masses 
of  conglomerate  in  a  sand  or  clayey  matrix  are  some- 
times found  in  various  pits.) 

Stifr_  blue  clay      1ft.  to  1ft.     6in. 

Milk-white  sand  occasionally  clayey  in  the  upper  part. 

Bed  of  pebbles  in  which  stream-tin  is  said  occasionally  to  occur. 


20        IV.  A.  E.  Ussher— Post- Tertiary  Geologi/  of  Cornwall. 

The  followinjij  section  on  the  North  of  the  Beacon  is  given  by  Dr. 
Boase  (Trans.  K.  Geol.  Soc.  Corn.  vol.  iv.  p.  2'JG) : 

(9)    1.    Subsoil  -  earth  with  angular  stones      1ft.  to  2ft.     Oin. 

2.  Yellow  and  white  sand,  with  minute  particles  of  schorl 

3.  Dark   ochreous-coloured  sand,  with  a  minute  quantity 

of  clay  between  the  grains      2ft.     Oin. 

4.  Soft   and '  greasy,  tough,  adhesive  blue  clay,  with   an 

oily  rancid    smell,    as    if    from   impregnation   of 

animal  matter 1ft.     Oin. 

5.  Clay  (called  Furnace  clay),  white  and  plastic,  emitting 

an   argillaceous   odour     3ft.     Oin. 

6.  Sand,  neaily  pure  white  .. 7ft.     Oin. 

7.  Loose  rubbly  layer,  like  (1),  said  to  rest  on  solid  rock. 

(10)  Qnoted  by  Mr.  Henwood  (op.  cit.)  from  the  Mining  Review, 
paper  by  Jlr.  Thoma.s  : — Section  on  the  Nortli  of  the  Beacon,  half  a 
mile  from  it,  near  Wheal  Kind.  Surface  383  feet  above  high  water. 
Eigbt  feet  sunk  in  white  sand  (7  feet  below  the  surface). 

(11)  ]\Ir.  Henwood  quotes  (op.  cit.)  the  following: — N.W.  from 
the  Beacon.  Surface  at  377  feet  above  liigh  water.  Sand  met  with 
at  3  feet  below  the  surface  :   15  feet  sunk  through  yellow  sand. 

(12)  Messrs.  Kitto  and  Davies  give  the  following  section  to 
N.W.  of  the  Beacon  : 

Soil  and  Head 4ft.  Oin. 

Blue  fire  clay  (coarse,  through  admixture  of  sand)     7ft.  Cin. 

Candle  clay,  adhesive  and  very  tough    2tt.  Cm. 

Sand  resting  on  Killas      6ft.  Oin. 

(13)  Mr.  Hawkins  (op.  cit.)  gives  the  following  section  on  the 
East  of  the  Beacon  : 

Depth  of  the  deposit,  24  feet  in  all. 

Yellow  Cobb  under  vegetable  mould 

Yellow  sand 

Mining  clay 

AVhite  sand    

A  few  flatfish  pebbles  in  black  mud  (local  name)     ... 

(14)  Messrs.  Kitto  and  Davies  give  the  folic 
east  of  the  Beacon  (op.  cit.)  : 

Head     

White  candle  clay       

Gravel     

White  candle  clay       

Yellow  and  whitish  sand  not  gone  throng' 

The  following  sections  were  taken  in  the  isolated  part  of  the, 
deposit  on  granite  to  the  West  of  the  Beacon  : 

(15)  Hawkins  (op.  cit.) — 

Yellow  Cobb     4ft.    Oin.  I 

Clay    6tt.    Oin. 

Puddle  sand  (local  name) 2ft.  to  3ft.    Oin. 

(16)  Henwood,  quoted  from  Mining  Review  (op.  cit.): — Surface! 
418  feet  above  high  water.  Sand  met  with  at  9  feet  below  the 
surface;  12  feet  sunk  through  yellow  sand  of  a  lighter  tint  at  the 
base. 


2ft.  to  3ft. 

Oin. 

3ft.  to  4ft. 

Oin. 

1ft. 

2in. 

4ift.  to  5ft. 

Oin. 

2ft.  to  3ft. 

Oin. 

section  on 

the 

...      6ft. 

Oin. 

...      3ft. 

Oin. 

...      ]ft. 

Oin. 

...       2ft. 

6in. 

9ft. 

Gin. 

20ft. 

Oin, 

Oft. 

Sin 

2ft. 

Oin. 

3ft. 

Oin 

TF.  A.  E.  Ussher — Post- Tertiary  Geology  of  Cornwall.       21 

(17)  Messrs.  Kitto  and  Davies  (op.  cit.)  : 

Head        

Candle  clay      

Dark  red  sand 

Yellowish  sand        

Gravel,  pebbles,  boulders,  and  sand  resting  on  granite 

34ft     3in. 

I  observed  four  pits,  all  in  the  main  deposit,  and  lying  to  the 
northward  of  the  Beacon,  varying  from  seven  to  eleven  feet  in 
depth  ;  the  very  impersistent  nature  of  the  clay  and  of  the  colours 
in  the  sands  was  very  noticeable. 

From  the  map  and  sections  accompanying  the  paper  by  Messrs. 
Kitto  and  Davies  {op.  cit.),  it  will  be  seen — that  the  clays  are  in  no 
place  coextensive  with  the  sands,  although  in  parts  their  boundary 
approaches  very  near  to  the  limits  of  the  dejjosit ;  that  they  are  the 
thickest  in  the  isolated  patch  on  the  granite  (17),  which  lies  in  a 
basin  ;  that  the  coarse  detritus  is  of  exceptionally  local  cliaracter 
in  the  different  sections,  tin  stone  pebbles  being  confined  to  the 
immediate  vicinity  of  lodes.  The  appearances  of  bedding  in  the  sand, 
and  the  relative  positions  of  the  sands  and  clays  in  sections  (1), 
(7),  and  (8),  are  indications  of  a  continuity  of  deposit,  which  the 
variability  of  the  other  sections  given  shows  to  be  abnormal.  The 
occurrence  of  quartz  pebbles  in  exceptionally  sandy  overburden 
(section  6),  is  worthy  of  note,  and  suggests  the  former  overspread  of 
gravelly  detritus,  similar  to  the  gravels  of  Crousa  Down  and 
Crowan. 

The  Head,  as  far  as  I  observed  it,  consists  of  bi'own  loam,  with 
angular  fragments  of  local  rocks  derived  from  the  hill  above, 
resembling,  according  to  Messrs.  Kitto  and  Davies,  "  The  soil  and 
subsoil  found  upon  the  Killas  of  Cornwall,  except  that  it  is  some- 
what sandy  in  parts  and  occasionally  contains  washed  pebbles." 
This  Head,  Overburden,  or  Cobb,  is  of  like  nature,  and  probably 
roughly  contemporaneous  with  the  accumulations  of  stony  loam  on 
the  coasts  hereafter  to  be  noticed.  The  preservation  of  the  deposits 
in  their  present  form  is  jDrobably  largely  due  to  this  protecting 
envelope  of  talus  shed  Irom  the  adjacent  Beacon  hill,  which  ex- 
ceeds 600  feet  in  height. 

From  such  local  materials  as  the  gi'anite  on  the  west  of  the 
Beacon,  the  Elvan  Course  to  the  north  of  it,  and  the  Killas,  the 
sands  and  clays  seem  to  have  been  formed. 

The  position  of  the  deposits  with  reference  to  the  present  coasts, 
and  to  tlie  higli  land  of  the  Beacon,  and  the  cliff-like  sections  and 
waterworn  hollows  noticed  in  some  parts,  would  seem,  "as  De  la 
Beche  suggests,"  to  justify  a  marine  origin,  but  with  them  "  the 
resemblance  to  the  raised  beaches  appears  to  terminate"  (Keport, 
page  258.)  The  interchangeable  characters  of  the  sands  and  clays 
are  more  in  accordance  with  the  irregular  deposition  of  a  stream, 
subject  to  fluctuations  attendant  on  meteorological  changes,  than  with 
the  more  uniform  sorting  action  of  a  coast-fringing  sea.  The  very 
local  character  of  the  basement  gravels  is  also  against  the  admission 


22        W.  A.  E.  Ussher— Post- Tertiary  Geology  of  Cornwall. 

of  a  marine  origin.  As  an  entirely  new  system  of  drainage  has 
been  moulded  since  the  deposits  were  thrown  down,  proximity  to 
the  present  coast-line  is  no  argument  in  favour  of  marine  origin  or 
former  proximity  to  the  sea. 

riuviatile  agencies,  which  have  produced  similar  effects  in  wear- 
ing tlie  surface  of  the  shelf  in  stream-tin  sections,  coupled  with  the 
weathering  and  water- wear  of  a  vertical  ftice,  slickenside,  or  joint, 
might,  in  the  absence  of  further  evidence,  explain  the  phenomena 
of  the  smoothed  surfaces,  water-worn  hollows,  and  old  cliff  face 
mentioned  by  Messrs.  Kitto  and  Davies.  Had  such  action  pre- 
vailed for  a  long  period  in  an  old  line  of  drainage  down  which  the 
coarser  detritus  had  been  swept,  the  damming  up  of  the  old 
stream  course  and  selection  of  a  new  one  above  the  present  site  of 
the  deposits,  would  tend  to  the  formation  of  a  lake  in  whose  quiet 
waters  the  finer  debris  of  the  adjacent  land  borne  down  by  rills  and 
streamlets  would  have  been  filtered,  and  have  settled  down  in  the 
form  of  sand  and  clay. 

The  isolated  positions  of  the  deposits  of  Crousa  Down,  Crowan, 
and  St.  Agnes,  afford  no  clue  as  to  their  relative  ages.  Yet  tliis 
isolation  justifies  me  in  classifying  them  together  as  the  oldest  super- 
ficial deposits  as  yet  noticed  in  Cornwall.  An  entire  bouleversement 
of  tlie  levels  of  their  respective  districts  has  taken  place  since  their 
formation,  and  all  traces  of  synchronous  deposition  have  been  swept 
away  in  the  elaboration  of  the  present  drainage  system.  As  they 
can  onlj'  be  regarded  as  relics  of  much  more  widespread  deposits, 
the  possibility  presents  itself  that  we  may  have  in  them  the  traces,  ■ 
in  sita,  or  re-distributed,  of  Tertiary  or  even  late  Cretaceous  deposits,  , 
1^ resenting  a  different  aspect  to  that  in  other  areas  through  de-  < 
jiendence  on  loeal  sources  of  supply.  Daring  the  vast  jieriod  that 
intervened  between  the  Culm-measure  rocks  and  the  Pleistocene 
Age,  it  is  unreasonable  to  argue  from  the  absence  of  deposits  of 
intermediate  age  that  Cornwall  was  never  invaded  by  Secondary  or 
Tertiary  seas. 

On  the  Occurrence  of  Flints  in  Cornicall. — De  la  Beche  (Eeport, 
p.  429)  commented  on  the  abundance  of  rolled  Chalk  flints  in  the 
recent  as  well  as  the  liaised  beaches  on  the  Cornish  coast ;  he 
suggested  the  existence  of  a  race  making  use  of  flint  implements 
prior  to  the  raising  of  the  beaches,  and  tliat  these  flints  in  trans- 
port from  the  localities  whence  they  were  derived,  might  have  been 
dropjied,  and,  in  unlading,  have  been  lost  and  rolled  with  the  beach 
pebbles.  This  theory  may  be  dismissed  as  untenable  both  on 
account  of  the  absence,  in  inland  localities,  of  relics  of  such  a  race 
as  that  invoked,  and  on  account  of  the  number  of  natural  flints  and 
the  absence  of  signs  of  manufacture. 

Jlr,  Peach  notices  (T.Pi.G.S.  Corn.  vol.  v.  p.  55)  the  abundance  of 
flints  in  some  of  the  coves  at  Gornin.  and  suggests  their  derivation 
from  the  Chalk  of  "No  Kest,"  f)ff  the  Dodnian  Point,  "a  name  given 
to  some  submarine  rocks  by  the  fishermen,  owing  to  their  trawls 
becoming  hitched  in  the  rough  ground." 

It  is  scarcely  credible  that  such  observers  as  De  la  Beche,  Borlase, 


W.  A.  E.  ITssher — Post- Tertiary  Geology  of  Cornwall.       23 

Boase,  Carne,  Henwootl,  etc.,  could  have  failed  to  notice  tlie 
existence  of  Cretaceous  rocks  off  the  Cornish  coast,  and,  if  known 
to  them,  they  would  certainly  have  coiuniented  upon  them.  There- 
fore, in  the  absence  of  further  particulars,  it  is  safer  to  regard  the 
"  Chalk  of  No  Kest "  as  a  local  epithet  without  any  geological 
significance. 

Do  la  Beche,  quoting  Borlase  (Nat.  Hist.  p.  106,  in  Report,  p.  646), 
says  :  "  In  the  low  lands  of  the  i:»arish  of  Ludgvan,  in  a  place  called 
Vorlas,  there  is  a  bed  of  clay,  about  three  feet  under  the  grass,  in 
which  numbers  of  chalk  flints  are  found,  with  pebbles  of  quartz 
and  some  shingle,  willi  pieces  of  angular  slate."  I  was  unable  to 
find  the  locality  indicated,  the  present  rector  of  Luclgvan  being 
ignorant  of  the  name.  Thinking,  however,  that  Vorlas  might  be  a 
misprint  for  Crowlas,  a  small  village  on  the  flats  near  Ludgvan,  I 
made  inquiries  there,  but  failed  to  elicit  any  information  respecting 
the  occurrence  of  flints  in  the  neighbourhood. 

Mr.  Henwood  (Journ.  11.  Inst.  Corn.  vol.  iv.  p.  214)  mentioned 
the  occurrence  of  flints  of  considerable  size  in  the  tin  ground  at 
Lower  Creamy,  a  part  of  Red  Moor,  in  Lanlivery,  N.  of  St.  Austell. 
He  also  slated  that  a  few  flints  have  been  very  rarely  found  in  a 
jeat  bed,  containing  remains  of  furze,  alder,  oak,  and  hazel,  in  the 
stream  works  of  Pendelow,  as  shown  in  1873  {op.  cit.  p.  213). 
Mr.  Higgs  (T.  H.  G.  S.  Corn.  vol.  vii.  p.  44'J)  gives  a  short  notice 
of  the  discovery  of  a  substance  resembling  a  chalk  flint  in  a  cavity 
in  a  lode  in  Balleswhidden  IMine. 

If  the  above  are  Cretaceous  flints,  and  not  fragments  of  slate  or 
fine  grit,  to  which  contact  with  igneous  matter  had  imparted  a 
cherty  character,  they  would  seem  to  indicate  the  destruction  of 
Cretaceous  material,  or  of  deposits  of  a  later  date,  resulting  in  part 
from  the  waste  of  Chalk. 

Mr.  A.  Smith  (T.  R.  G.  S.  Corn.  vol.  vii.  p.  343)  mentioned  the 
occurrence  of  comparatively  unworn  chalk  flints,  and  fragments  of 
Greensand  rock  more  worn,  on  Castle  Down,  in  Tresco,  one  of  the 
Scilly  Group. 

Mr.  Spence  Bate  (Trans.  Dev.  Assoc,  for  1866)  alludes  to  the 
occurrence  of  flints  in  moorland  around  Dosmare  Pool,  Curza 
(?  Crousa)  Down,  on  the  top  of  Maen  rock,  at  Constantiue,  and  on 
Trt'vose  Head. 

The  flints  occurring  in  the  Raised  Beaches  will  be  noticed  in  the 

section  devoted  to  the  latter  further  on. 

^        As  the  present  drift  of  shingle  from  W.  to  E.  is  the  reverse  of 

i|.  that  which  the  presence  of  chalk  flints  in  the  recent  beaches  would 

i_    lead  us  to  expect,  we  may  conclude  that  they  were  obtained  by  the 

destruction  of  the  raised  beaches,  and  explain  their  occurrence  in  the 

latter  by  either  of  the  following  hypotheses :  fii\st,  that  the   set  of 

the  wind-waves  during  the  formation  of  the  Raised  Beaches  was  the 

reverse  of  the  present,  as    Mr.   Godwin-Austen  suggests   (Q.J.G.S. 

vol.  vi.  p.  87)  ;  or,  secondly,  that  during   the  Pliocene   or  part  of 

the  Pleistocene  Period,  prior  to  the  formation  of  the  raised  beaches, 

the  laud  stood  at  a  much  greater  elevation,  and  the  English  Channel 


24        W.  A.  E.  Ussher — Post- Tertiary  Geology  of  Cornwall. 

valley  as  dry  land  "  served  to  connect  the  British  Islands  with 
France,  etc."  (Godwin-Austen,  op.  cit.) ;  that  a  large  part  of  its  area 
was  drained  by  rivers  and  streams  flowing  westward,  and  carrying 
Cretaceous  and  other  easterly  derived  detritus  in  that  direction, 
which  detritus,  on  the  submergence  of  the  valley,  was  incorporated 
by  the  Pleistocene  sea  in  the  beaches  then  successively  marking  its 
advance,  till  the  culmination  of  the  subsidence  at  levels  marked  by 
the  Kaised  Beaches. 


Notes  on  Glacial  Hi/potheses. 

Although  the  Glacial  epoch  has  left  no  direct  evidences  of  its 
changes  in  Devon  and  Cornwall,  it  is  scarcely  possible  that  eitlier 
county  remained  uninfluenced  by  them.  The  very  fragmentary 
relics  of  deposits  formed  during  the  existence  of  a  previous  and  very 
different  configuration  seems  to  call  for  S(;rae  such  powerful  denuding 
agencies  as  torrential  surface  waters,  consequent  on  the  termination 
of  rigorous  conditions  of  climate. 

The  Kev.  0.  Fisher  (Gkol.  Mag.  1873,  Yol.  X.  p.  163)  ascribes  the 
reversal  of  lamiufe  in  schorlaceous  granite,  in  Carclaze  Mine,  to  the 
passage  of  ice  over  them.  But  such  phenomena,  as  I  have  elsewhere 
(Q  J  G.S.  1878,  vol.  xxxiv.  p.  49)  endeavoured  to  show,  furnish  no 
proofs  of  ice-action  in  the  South-west  of  England.  Striag  or 
nioutonneed  surfaces  have  not  been  detected  in  Devon  or  Cornwall. 
The  grooved  face  of  rock  near  Barlynch  Abbey,  Nortli  Devon, 
ascrilied  by  Prof.  Jukes  to  ice-action  (Geol.  Mag.  Vol.  IV.  p.  41  ; 
vide  Whitley,  32nd  Ann.  Eep.  R.  Inst.  Corn.),  is  merely  a  voluted 
bedding  plane,  a  structure  not  unfrequently  met  with  in  Devonian 
and  Culm-measure  rocks,  and  exhibited  by  some  beds  in  an  adjacent 
quarry. 

If  Cornwall  was  at  any  time  subject  to  extreme  glacial  conditions, 
its  highlands  were  not  submerged  during  the  Glacial  epoch,  nor 
were  its  borders  invaded  by  a  foreign  ice-sheet ;  for  traces  of 
submergence  would  be  found  in  the  one  case,  and  foreign  ice-borne 
materials  in  the  other.  Positive  evidences  of  local  glaciation  are 
also  wanting,  unless  we  regard  the  presence  of  large  boulders  at 
high  levels,  as  the  diallage  blocks  of  Crousa  Down  for  instance,  as 
the  unremovable  debris  of  an  old  glacier  system,  and  ascribe  the 
presence  of  large  boulders,  at  some  distance  from  their  parent  rocks, 
in  river  gravels,  to  the  relics  of  moraine,  carried  down  to  successively 
lower  levels  in  the  excavation  or  deepening  of  the  present  lines  of 
drainage.  However,  if,  as  I  agree  with  Mr.  Godwin- Austen  in 
thinking  (op.  cit.),  the  land  stood  at  a  much  greater  elevation  during 
the  Glacial  epoch,  a  gi-eat  and  constant  snowfall  may  have  given 
rise  to  local  glacier  systems ;  and  as  the  present  area  of  the 
county  would  offer  little  more  than  the  generative  sources  of  the 
(imaginary)  glaciers,  all  traces  of  pre-existent  deposits  and  of 
moraine  matter,  except  very  large  boulders,  would  be  swept  down 
by  the  flood  waters  of  the  succeeding  period  of  subsidence  to  levels 


W.  A.  E.  Ussher — Fod-Teriiary  Geology  of  Cornwall.       25 

now  submerged.  But,  as  all  such  glacial  theories  are  purely 
hypothetical,  it  behoves  one  to  fall  back  on  the  probability  that 
Cornwall,  during  the  Glacial  epoch,  stood  at  a  much  greater 
elevation,  and  that  its  highlands  were  crowned  with  constant  snows, 
the  melting  of  which  during  the  succeeding  amelioration,  accom- 
panied by  suljsidence,  caused  the  liberation  of  great  quantities  of 
surface  water  with  torrential  power  carrying  oft"  the  pre-existing 
detritus  to  lower  lands,  now  submerged. 


PART    III. 

THE    EAISED    BE^^^i^CHES 

AND    ASSOCIATED    DEPOSITS    OF    THE    CORNISH    COAST. 


THE    following  observations  of  the  Cornish  Cliffs  are  given  in 
order,  proceeding  round  the  coast  from  Plj'mouth.     The  num- 
bers and  letters  have  been  prefixed  to  facilitate  subsequent  reference. 

1.  Mount  Edgecombe,  near  Plymouth. 

a.  De  la  Beche  (Geological  Manual,  p.  159)  mentions  the  occur- 
rence of  rolled  shingles,  covered  by  fragments  of  slate  and  red 
sandstone  near  Bedding  Point ;  the  height  of  the  deposit  is  not  given. 

h.  Near  Mount  Edgecumbe  Obelisk  I  noticed  brown  and  reddish 
coarse-grained  sand  filling  an  inequality  in  the  limestone  at  about 
30  feet  above  the  river ;  tliis  is  probably  a  trace  of  contemporaneous 
deposition  with  the  Hoe  Baised  Beach. 

2.  Looe  Island.  Mr.  Pengelly  (Trans.  E.  G.  S.  Corn.  vol.  vii.  p. 
118}  noticed  the  occurrence  of  layers  of  comminuted,  and  somewhat 
rounded,  yellowish  matter  containing  rather  large  rounded  slate 
fragments  and  ordinary  pebbles,  on  the  northern  cliffs  of  the  island. 
Height  above  high  water  not  given. 

3.  St.  Austell's  Bay. 

a.  A  point  at  which  Baised  Beach  is  engraved  on  the  map,  at  Pol- 
kerris,  is  capped  by  8  feet  of  Head  of  small  angular  killas  fragments ; 
occasional  quartz  pebbles  were  found,  being  either  the  relics  of  a 
raised  beach,  or  hurled  to  a  height  of  30  feet  above  high-water 
mark  by  storm  waves  from  the  beach  below.  This  point  is  joined  to 
the  main  cliff  by  a  very  narrow  ridge  of  rock. 

h.  Near  Pol  mere  the  Head  rests  upon  micaceous  slates,  and  in 
places  presents  a  rudely  stratified  appearance. 

4 


26       TF.  A.  E.  Ussher— Pod-Tertiary  Geology  of  Cornwall. 

c.  Near  the  Par  Inn,  a  stratified  gravel  of  subangular  grit,  quartz, 
slate,  and  granite  stones,  and  occasional  boulders,  4  to  5  feet  ia 
thickness,  occurs  at  about  20  feet  above  high  water. 

d.  On  the  south  side  of  Spit  Point,  fine  gravel  -with  pebbles  of 
quartz  and  boulders  (one  flint  pebble  found,  and  a  fragment  of  Car- 
dium,  ?  in  situ)  8  feet  in  thickness,  and  at  base  o  feet  above  high 
water,  occurs  on  the  low  cliffs. 

e.  Near  the  above  the  base  of  the  raised  beach  is  10  feet  above 
high  water ;  it  consists  of  fine  gravel  alternating  with  greyish  sand, 
upon  large  pebbles  and  imworn  blocks  of  the  subjacent  rock.  The 
deposit  is  10  feet  in  thickness,  the  layers  appear  to  dip  seaward. 

4.  Gerran's  Bay. 
a.  On  the  eastward  side  of  the  beach  the  section  consists  of — 

Brown  soil  with  angular  stones       5ft.     Oin. 

Brown  loam  with  anfi:ular  fragments  of  slate  and  quartz     ...  10ft.     Oin. 

Beds  of  consolidated  black  sand  and  quartz  gravel,  lying 
unevenly  on  the  subjacent  rock  at  about  five  feet  above 
high  water      4ft.     Gin. 

De  la  Beche  (Eeport,  p.  430)  mentions  the  consolidation  of  portions 
of  the  raised  beach  in  Gerran's  Bay  by  oxide  of  iron.  Near  Pen- 
dowa  the  beach  is  absent,  and  the  Head  rests  directly  on  the  slates. 

h.  Mr.  Trist  (T.  E.  G.  S.  Corn.  voL  i.  p.  Ill)  described  the  raised 
beach  as  a  flat  stratum  of  sand  and  pebbles,  sometimes  occumng  as 
a  black  sandstone  2  feet  in  thickness,  sometimes  as  a  conglomerate 
of  sand  and  pebbles  10  feet  thick,  resting  on  limestones  and  argil- 
laceous schists  abounding  in  manganese,  and  capped  b}^  an  argilla- 
ceous friable  earth. 

c.  Near  Pendover  (?  Pendowa)  beach,  Mr.  Trist  noticed  quartz 
boulders  at  the  Carnes,  wholl}'  insulated,  and  of  a  different  nature 
from  the  substratum  {ride  T.  E.  G.  S.  Corn.  vol.  vi.  p.  91.  Budge.) 

d.  Dr.  Boase  (T.  E.  G.  S.  Com.  vol.  iv.  pp.  270,  273)  mentions  the 
occurrence  of  "  layers  of  different  substances  "  in  the  cliffs  to  the 
east  of  Porthscatho  and  in  Gerran's  Bay,  the  inferior  10  feet  being 
much  consolidated.  One  ferruginous  layer  resembled  pudding-stone. 
The  pebbles  diminish  upwards  into  pure  sand,  reddish  brown  and 
friable,  in  layers  8  or  9  inches  thick. 

e.  (op.  cit.  p.  275.)  At  Porth,  one  mile  east  of  St.  Anthony,  Dr. 
Boase  noticed  beds  of  sand  and  gravel ;  Porth  farmhouses  being  built 
on  diluvium  of  regular  beds  of  sand  and  pebbles,  the  latter  below ; 
shells,  chiefly  marine  univalves,  were  found  in  parallel  layers  in  the 
sand.     The  height  above  high  water  is  not  given. 

5.  Falmouth. 

a.  Coast-section  on  the  N.E.  of  Pendennis  Castle.  Head  of  angular 
fragments  of  slate  and  (quartz  witli  a  tolerably  regular  horizontal  lie, 
40  to  50  feet  in  thickness,  contains  here  and  there  a  few  pebbles  at 
its  base,  which  is  from  5  to  10  feet  above  high  water.  Mr.  Godwin- 
Austen  mentioned  (Q.J.  G.  S.  vol.  vii.  p.  121)  the  occurrence  of  30 
feet  of  Head  on  the  west  of  Pendennis  Point. 

6.  Near  Cove  Battery  the  Head  is  of  a  greyish  colour  in  the  upper 


W.  A.  E.  Ussher— Post- Tertiary  Geology  of  Cornwall.        27 

part,  brownish,  below ;  a  line  of  larger  fragments  and  a  band  of  loam 
without  stones  occur  in  it. 

c.  Mr.  K.  W.  Fox  (Phil.  Mag.  and  Journ.  Science,  ser.  3,  vol.  i.  for 
1832,  p.  471)  describes  the  Falmouth  raised  beach  as — a  horizontal 
bed  of  rolled  quartz  pebbles,  gravel  and  sand  (like  the  present 
beach),  from  1  to  3  feet  in  thickness,  and  generally  from  9  to  12  feet 
above  the  highest  spring  tides.  The  Head  upon  the  old  beach  is 
described  as  earth,  stones,  and  detached  pieces  of  rock.  The  cliffs 
are  from  30  to  60  feet  in  height.  The  old  beach  does  not  extend  far 
from  the  cliff  face ;  it  was  observed  in  one  place  at  8,  in  another  at 
20  feet,  within  it.  Between  the  parishes  of  Budock  and  Mawnau 
the  pebbles  appeared  to  be  cemented  into  a  conglomerate,  in  places, 
by  the  oxides  of  iron  and  manganese. 

d.  Mr.  Godwin-Austen  (T.  G.  S.  ser.  2,  vol.  vi.)  describes  the  old 
beach  and  overlying  Head  at  Swanpool  as — purely  marine  beds  pass- 
ing up  into  fluvio-marine  and  fluviatile  accumulations. 

e.  Between  Pennance  Point  and  Maen  Porth  (Fig.  1),  a  bed  of 
pebbles,  chiefly  quartz,  with  slate  boulders,  is  visible,  under  Head  of 
angular  fragments  in  loam,  at  intervals.  In  one  place  the  beach 
consists  of  quartz  pebbles  in  grey  and  reddish  brown  sand,  with, 
large  worn  blocks  of  slaty  rocks ;  it  is  3ft,  6in.  thick,  and  about  4 
feet  above  high  water  at  its  base.  Eock  platforms  are  noticeable  at 
about  the  level  of  spring  tide  high  water. 


Fig.  1. — The  Coast  toward  Rosemullion  Head;  showing  Rock  Platforms  and  Cliffs 
composed  of  Head  upon  Raised  Beach. 

6.  South  of  the  R.  Helford. 

a.  At  Ligwrath,  between  Nare  Point  and  Porthalla,  the  Head  con- 
sists of  brown  earth  with  angular  stones ;  pebbles  are  met  with  iu 
places  at  its  base,  at  about  5  feet  above  high  water.  Boulders  com- 
pose the  present  beach, 

h.  South  of  the  above,  traces  of  a  raised  beach  consisting  of  beds 
of  coarse  black  and  brown  sand,  with  grit,  slate,  igneous  rock,  and 
small  quartz  pebbles,  in  places  2  to  3  feet  thick,  and  at  base  about 
8  feet  above  high  water,  are  visible  here  and  there  under  Head  of 
grey  and  brown  loam  with  angular  stones. 


28        TF.  A.  E.  Ussher— Pod- Tertiary  Geology  of  CormcaU. 

c.  De  la  Beche  (Report,  p.  431)  figures  part  of  a  consolidated 
raised  beach  forming  the  roof  of  a  cavern  in  the  slates  on  which  it 
rests,  and  supporting  a  Head  of  angular  fragments,  between  Port- 
halla  and  the  Nare  Point.  He  also  gives  a  sketch  of  the  old  beach 
at  Nelly's  Cove  and  between  EosemuUion  Head  and  Mainporth  {op. 
cit.  p.  432). 

d.  The  Rev.  E.  Budge  (T.  E.  G.  S.  Corn.  vol.  vi.  p.  1)  mentions 
the  occurrence  of  a  raised  beach,  about  5  feet  above  high  water,  con- 
tinuing for  some  hundreds  of  yards  from  Nelly's  Cove  (^  mile  from 
Porthalla),  and  accessible  only  at  low  water;  he  observed  traces  of 
the  old  beach  on  steep  rock  ledges  now  overflowed  by  the  tide.  On 
the  north  of  Nare  Point,  8  to  10  feet  of  angular  debris  rested  on  the 
old  beach. 

7.  Coverack  Cove. 

•  a.  The  low  cliffs  to  the  east  of  Carnsullan  are  about  15  feet  in 
height,  and  composed  of  brown  earth  with  angular  and  subangular 
stones  and  boulders. 

h.  The  Eev.  E.  Budge  {op.  cit.)  describes  the  cliff-section  on  the 
north  side  of  the  Cove  as — Eeddish-coloured  marl  or  rubble  upon  a 
thick  bed  (12  feet)  of  fine  ferruginous  sand,  consolidated  in  places, 
upon  large  rolled  pebbles  arranged  in  regular  lines  and  about  5  feet 
above  high  water  at  their  base. 

c.  The  same  observer  says  that  the  whole  of  the  outer  portion  of 
the  Lowlands  in  St.  Keverne  parish  (a  flatfish  tract  of  60  acres  in 
extent)  is  formed  of  very  fine  sand  (valued  for  constructing  moulds 
for  brass  casting),  so  similar  to  that  overlying  the  Coverack  raised 
beach  that  he  considered  them  contemporaneous.  At  and  near  the 
coast-line  pebbles  were  occasionally  met  with  in  the  sand. 

d.  Mr.  Budge  mentions  a  rampart  of  large  diallage  pebbles  round 
a  low  fortress  of  sand  upon  the  present  beach  at  Coverack. 

e.  Dr.  Boase  (T.  E.  G.  S.  Corn.  vol.  iv.  p.  329)  mentions  the  occur- 
rence of  diluvium  of  an  ochreous  colour,  consolidated  toward  its  base, 
and  containing  small  pebbles  of  quartz,  compact  felspar,  and  serpen- 
tine, resting  on  serpentine,  near  Coverack  Quay. 

/.  De  la  Beche  (Report,  p.  429)  and  Godwin- Austen  (Q.  J.  G.  S.  . 
vol.  vii.  p.  121),  comment  on  flints  occurring  in  the  Coverack  raised 
beach.     Flints  also  occur  in  the  j^resent  beach  at  Porthbeer  Cove, 
Bouth  of  Coverack. 

8.  Gunwalloe.  The  cliff's  are  capped  in  places  by  a  Head  of  light 
brown  loam  with  angular  stones. 

The  Lizard  District  south  of  a  line  between  Porthbeer  Cove  and 
Mullion  was  not  observed  by  me,  nor  can  I  find  any  descriptions  of 
Pleistocene  phenomena  on  its  sea-board. 

The  low  cliff's  to  the  south  of  the  Loo  bar  are  capped  by  about 
5  feet  of  brown  loam  with  angular  fragments  of  quartz,  etc.,  under 
coarse  brownish  blown  sand. 

9.  Coast  from  Loo  Pool  to  Marazion. 

a.  De  la  Beche  (Report,  p.  430)  figures  part  of  a  raised  beach  be- 
tween the  Loo  Pool  and  Cove  village,  stained  by  black  oxide  of  iron, 


W.A.E.  Ussher— Pod-Tertiary  Geology  of  Cornwall.        29 

and  containing  strings  of  the  same  substance,  the  prevalence  of  which 
in  the  rocks  of  South  Cornwall  is  pointed  out. 

b.  Mr.  Henwood  (T.  R.  G.  S.  Corn.  vol.  v.  p.  54)  noticed  patches 
of  granite  and  slate  pebbles,  from  the  size  of  a  nut  to  a  foot  in 
diameter,  in  Tremearne  Cliff.  The  deposits  rested  on  slates  at  14  feet 
above  the  present  beach,  in  one  spot,  and  at  30  feet  in  another,  going 
eastward. 

c.  {op.  cit.)  "At Wheal  Trewavas,  where  the  rock  is  wholly  com- 
posed of  granite,  it  is  covered  by  a  thick  bed  of  transported  frag- 
ments of  micaceous  slate." 

d.  On  the  west  of  Pra  Sands,  Mr.  Henwood  (op.  cit.)  noticed  a 
bed  of  granite,  elvan,  and  slate  pebbles,  at  about  6  feet  above  the 
present  beach,  and  covered  by  "a  high  bank  of  rubbish,"  the  debris 
of  the  adjacent  rocks. 

e.  Between  Cuddan  Point  and  Trevean  Cove,  the  Head  consists 
of  dark  grey  loam  with  angular  (local)  fragments. 

/.  The  Perran  Sands  are  bounded  by  cliffs,  from  5  to  20  feet  high, 
partly  composed  of  brown  loam  with  angular  stones  and  blocks  of 
greenstone. 

g.  In  a  cove  west  of  Perran  Sands  and  south  of  Perranuthno ;  in 
one  part — 

Brown  earth  with  large  and  small  angular  stones 10ft.  to  15ft. 

upon — large  pebbles  and  subangular  fragments  of  quartz  and 

greenstone      1ft. 

upon — brown  loam  with  small  angular  quartz  stones  and  large 
angular  greenstone  boulders. 
g'.  In  another  place — 

Soil     2ft.  to  3ft. 

Brown  loam  with  angular  greenstone  fragments    6ft.  to  7ft. 

As  above,  fragments  fewer,  and,  as  a  rule,  smaller       10ft.  to  15ft. 

Pebbles,  and  occasionally  subangular  fragments,  of  quartz 
and  greenstone 2ft.  (about). 

resting  unevenly  upon  greenstone,  at  from  8  to  12  feet  above  high 
water. 

7*.  Toward  Marazion  the  cliffs  average  20  feet  in  height,  and  are 
composed  of  a  Head  of  angular  slate,  quartz,  and  greenstone  frag- 
ments in  brown  loam. 

10.  South  of  Penzance. 

a.  Mr.  Carne  (T.  E.  G.  S.  Corn.  vol.  iii.  p.  229)  observed  layers  of 
pebbles  and  boulders  from  3  to  6  feet  thick,  and  40  feet  in  length,  at 
the  junction  of  the  slate  and  granite  at  Mousehole.  Mr.  Henwood 
gives  the  height  of  the  above  as  a  little  above  high-water  mark. 
{Ibid.  vol.  V.  p.  110.) 

The  following  are  from  Mr.  Game's  paper  (op.  cit.). 

b.  At  Carn  Silver,  boulders  and  pebbles  were  found  in  the  end  of 
a  cavern,  8  feet  wide  and  12  feet  high,  once  probably  filled  with 
them. 

c.  In  St.  Loy  Cove,  under  30  feet  of  Head  of  granitic  stones  in 
clay,  pebbles  and  boulders  were  observed,  4  to  8  feet  in  thickness, 
150  feet  in  length,  and  at  their  base  at  high-water  mark.  (Present 
beach  composed  of  granite  boulders. — W.U.) 


30         W.  A.  E.  Ussher— Post- Tertiary  Geology  of  Cormcall. 

d.  Boulders  were  also  observed  at  Polwarnon  (?  Polguarnon)  Cove, 
Lean  Scath,  Pednvounder  Cove  (near  the  Logan  i-ock),  and  at  the 
Land's  End  Hole ;   but  their  height  above  the  sea  is  not  given. 

e.  Near  Penberth  on  the  east,  I  noticed  a  small  patch  of  Head 
composed  of  brown  loam  with  angular  stones  and  angular  and  sub- 
angular  boulders. 

11.  Land's  End. 

a.  In  Whitesand  Bay,  near  Carn  Aire,  the  Head  consists  of  angular 
and  subangular  fragments  and  boulders  of  granite  in  coarse  light  buff- 
brown  granitic  debiis  (growan),  becoming  browner  and  more  loamy 
near  the  base.     The  present  beach  is  composed  of  granite  boulders. 

h.  Between  Creagle  and  Aire  Points,  Mr.  Carne  (op.  cit.)  observed 
6  feet  of  boulders  and  pebbles  under  30  feet  of  clay  with  granitic 
fragments.     Base  of  boulder  bed  at  about  spring  tide  high  water. 

c.  On  the  south  of  the  Xanjulian  Eiver  (Carne,  op.  cit.)  boulders 
and  pebbles  occur  at  15  feet  above  high  water. 

d.  On  the  south  of  Pol  Pry  (oj).  cit.),  a  thin  bed  of  boulders  at  20 
feet  above  high  water. 

e.  In  an  iron  vein  at  Huel  Oak  Point  (op.  cit.)  boulders  were 
found  at  8  feet  above  high  water. 

12.  Pornanvon  and  Porth  Just. 

a.  In  Pornanvon  Cove  Mr.  Carne  (op.  cit.)  noticed  2  boulder  beds 
(in  a  matrix  of  calcareous  sand,  granitic  gravel  and  clay),  separated 
by  a  mass  of  solid  granite.  The  westernmost  bed  being  4  chains 
long,  10  feet  thick,  and  overlain  by  60  feet  of  granitic  debris  ;  that 
on  the  east  was  found  to  be  9  chains  long,  20  feet  in  maximum  thick- 
ness, and  surmounted  by  20  to  50  feet  of  granitic  debris.  The 
boulders  vary  in  size  from  that  of  a  hazel  nut  to  3  feet  in  diameter; 
no  large  slate  boulders  were  noticed.  The  base  of  the  deposit  is 
about  the  level  of  very  high  spring  tides.  At  Porth  Just  Mr.  Carne 
found  boulders  at  15  feet  above  high-water  mark. 

h.  Mr.  Hen  wood  (T.  E.  G.  S.  Corn.  vol.  v.  p.  13)  mentioned  the  oc- 
currence of  rounded  stones  of  granite,  from  the  size  of  a  nut  to  2  or 
3  feet  in  diameter,  with  a  few  slate  pebbles,  and  with  granitic  sand 
filling  the  interstices,  at  from  15  to  20  feet  above  high  water,  at 
Porth  Just  and  Pornanvon.  He  says  that  an  adit  at  "Wheal  Besans 
Lode,  Little  Bounds  Mine,  was  driven  for  several  fathoms  through 
one  of  these  beds,  which  was  found  to  be  from  GO  to  70  feet  in 
thickness.  (In  this  estimate  the  overlying  Head  was  probably 
included.— W.U.) 

c.  Miss  Carne  (T.  K.  G.  S.  Corn.  vol.  vii.  p.  371)  stated  that  the 
adit  of  a  mine  south  of  Kennal  Point  enters  the  cliifs  under  a  mass 
of  pebbles  and  boulders. 

13.  Cape  Cornwall. 

a.  In  the  south  part  of  Priest  Cove  I  noticed  a  few  pebbles  and 
subangular  stones  (one  of  granite),  in  olive-brown  loam,  and,  occa- 
sionally, greyish  sand,  under  50  to  60  feet  of  Head  which  presents 
a  stratiform  appearance  through  unequal  distribution  of  fragments, 
and  different  tints. 


W.  A.  E.  Ussher — Post-Tertiary  Geology  of  Cornivall.       31 

h.  In  a  little  cove  just  north  of  Cape  Cornwall,  I  observed  tho 
following  section  (Fig.  2)  : — 


Fig.  2. — Cape  Cornwall  on  the  North  side. 
1  Ineh=24  Feet. 

Head,  brown  loam  with  numerous  angular  stones,  containing 
larger  fragments  in  the  lower  5  feet,  with  pebbles  here 
and  there  at  and  near  the  base     13ft.     Oin. 

upon — gravel  of  pebbles  and  subangular  fragments  of  slate 
(altered),  quartz,  greenstone,  a  few  of  flint,  and  rounded 
and  subangular  granite  boulders,  in  coarse  brown  and  black 
loamy  sand     5ft.     Oin. 

Base  of  the  deposit  about  6  feet  above  high  water.  Boulders  on  the 
present  beach.    Kock  platforms  are  visible  at  about  high- water  mark. 

c.  In  Porthleden  Cove  the  following  section  was  taken : — 
Head,  brown  loam  with  small  angular  pieces  of  quartz,  containing 

small  fragments  of  slate,  and,  occasionally,  granite,  12  feet  thick ; 
upon  yellowish-brown  and  brown  loam  with  a  few  angular  frag- 
ments ;  upon  well-worn  and  subangular  boulders  with  a  few  large 
pebbles,  a  few  feet  above  high  water. 

d.  Mr.  Godwin-Austen  (Q.  J.  Gr.  S.  vol.  vii.  p.  121)  notices  the  oc- 
currence of  granite  pebbles,  under  yellowish  clay,  with  large  and 
small  angular  stones,  and  from  5  to  20  feet  in  thickness,  at  Creek 
Tor,  in  the  parish  of  St.  Just,  Penrith. 

e.  On  the  north  of  Cape  Cornwall,  Mr.  Came  (T.  E.  G.  S.  Com. 
vol.  iii.  p.  229)  noticed  a  bed  of  slate  boulders,  2  feet  thick,  and  a 
chain  in  length,  on  greenstone  at  10  feet  above  high  water.  The 
boulders  were  imbedded  in  clay  and  sand  with  small  slate  particles. 

14.  Pendeen  Cove  {op.  ciL).  Mr.  Carne  observed  3  feet  of  small 
pebbles  in  sand,  made  up  of  comminuted  marine  shells  and  pulverized 
granite,  in  one  place  capped  by  a  bed  of  sand,  overlain  by  GO  feet  of 
Head.  The  base  of  the  deposit  is  at  about  the  level  of  spring-tide 
high  water.  The  sand  is  in  process  of  consolidation  by  iron  oxide ; 
it  appears  to  have  been  blown  from  the  beach  into  the  interstices  of 
the  gravel. 

15.  St.  Ives. 

a.  On  the  east  of  Carrack  Olu  Point,  a  bed  of  pebbles,  1  foot  thick, 
is  shown  under  Head,  at  from  2  to  5  feet  above  high  water.  The 
greenstone  composing  the  Point  is  capped  by  a  Head  of  yellowish- 
brown  loam  with  angular  fragments  of  greenstone. 


32        W.  A.  E.  Ussher— Post-Tertiary  Geology  of  Cormcall. 

h.  In  the  bay  east  of  the  above,  near  the  north  part  of  St.  Ives, 
the  section  is  as  follows  : — 

Head,  with  large  angiilar  fragments       5ft.     Oin. 

Impersistent  strip  of  yellowish -brown  loam. 

Head,   loam  with  a  few  subangular  fragments,  and  boulders 

toward  the  base     4ft.     Oin. 

Olive  and  yellowish  sand  with  occasional  pebbles lOft.     Oin. 

At  base  about  5  feet  above  high  water ;  resting  upon  dark  bluish 
slaty  grit  with  numerous  joints. 

c.  On  the  north  part  of  St.  Ives  Island,  the  greenstone  is  capped 
by  a  Head  of  angular  greenstone  fragments  from  10  to  15  feet  in 
thickness. 

d.  Mr.  Whitley  (Journ.  E.  Inst.  Corn.  No.  11,  p.  181)  gives  the 
following  section  of  the  raised  beach  in  Porthgwidden  Cove,  St.  Ives  : 

Greenstone  soil,  upon  Head  of  large  angular  blocks  of  hornblendic  \  ^^^y^. 

rock.     Fine  sand  and  loam  ;  upon  pebbles  of  hornblendic  rock,  I  ^n  feet 

quartz,  granite,  and  a  few  worn  flints,  mixed  with  sand,  and  i  ,,  •  , 

containing  layers  of  fine  brown  sand  / 

The  base  of  the  deposit  is  given  as  5  feet  above  high  water. 

16.  Gwythian  and  Godrevy. 

a.  Near  the  southern  end  of  Black  Cliffs  the  slates  are  capped  by 
a  Head  of  brown  clay  with  angular  stones,  and  a  few  quartz  pebbles 
at  its  base. 

h.  South  of  Ceres  Rock,  greenish  grey  slates  are  capped  by  a  Head 
of  greenish  grey  clay,  probaljly  resulting  from  their  decomposition. 

c.  West  of  Gwythian  ;  cliflf-section — 


^iZ!y-i^^M\i\^s\\,-i; 


^-^A> 


Fig.  3. — Near  Gwythian.  Vertical  scale  1  inch  =  12  feet. 

1.  Blown  .sand 2ft.     Gin. 

2.  Brownish  loam  with  angular  slate  fragments 1ft.     Oin. 

3.  Agglomerate  of  angular  slate  and  quartz  stones  in  a  con- 

solidated matrix  of  small  angular  pieces  of  slate 3ft.     Oin. 

4.  Fine  brownish  sand,  consolidated  in  places,  containing  a 

few  pebbles         2ft.     Oin. 

5.  Three  beds  of  pebbles  and  subangular  stones  of  slate  and 

quartz,  with  occasional  pieces  of  flint  in  the  lower  bed. 

The  beds  are  4in.,  1ft.,  and  2ft.  in  thickness,  respectively     3ft.     4in. 

d.  Near  the  above,  the  Head  consists  of  grey  loam  with  angular 
slate  stones  of  small  and  average  size.     The  pebble  deposits  occur  in 


W.  A,  E.  Ussher — Post- Tertiary  Geology  of  Cornwall. 


33 


lOft.  to  20ft 
5ft. 


6ft. 


two  layers,  separated  by  a  seam  of  brown  sand.    The  base  of  the 
gravel  is  about  5ft.  above  high  water. 

The  following  observations  of  the  Cliffs  of  Godrevy  commence  at 
a  point  about  three-quarters  of  a  mile  to  the  south  of  Godrevy  Island. 
e.  The  section,  partially  obscured  by  sandy  debris,  consists  of — 
Head,  yellowish  and  grey  loam  with  small  angular  stones,  and 
occasional  large  angular  quartz  fragments,  resting  unevenly 

upon — fine  olive  brown  sand    

Coarse  grey  sand  with  pebbles  and  subangular  fragments  of 

slate  and  quartz,  the  former  sometimes  large     

Consolidated  coarse  blackish  sand  with  small  pebbles   and 

subangular  fragments,  and  a  few  large  pebbles 

At  base  5  to  8  feet  above  high  water. 

/.  The  pebble  band  is  stained  blackish ;  it  is  from  6  inches  to  1  ft. 
thick,  and  about  6  feet  above  high  water.  At  this  point  angular  and 
subangular  fragments,  some  large,  are  associated  with  the  pebbles  in 
a  coarse  impure  sand  matrix. 

g.  Two  beds  of  coarse  blackish  and  reddish-brown  consolidated 
sand,  containing  pebbles,  etc.,  of  slate  and  quartz,  3  feet  in  maximum 
thickness,  and  6  feet  above  high  water  at  their  base,  are  capped  by 
angular  Head.  The  upper  bed  forms  the  roof  of  a  cavern  in  the 
slates.     (Fig.  4.) 


variable. 


/S^S^-: 


■  Raised  Beach. 
Slate. 


Fig.  4.— Godrevy.        Vertical  scale — 1  inch  =  24  feet. 
h.  A  portion  of  the  consolidated  raised  beach  is  visible  on  tlie  fore- 
shore resting  upon  two  bosses  of  a  waterworn  slate  reef.    The  denu- 
dation of  the  reef  has  scarcely  affected  the  unsupported  part  of  the 
under  surface  of  the  beach.     (Fig.  5.) 


-^^ 


Fig.  5. — Godrevy  Beach. 
Portion  of  Raised  Beach  resting  on  bosses  of  Slate  isolated  from  the  main  cliff. 

5 


34       JF.  A.  E.  Ussher— Post-Tertiary  Geology  of  Cormcall. 

{.  Toward  Godrevy  Island  tlie  beach,  consists  of  coarse  blackish 
consolidated  sand  with  pebbles,  more  gravelly  at  the  base,  4  feet  thick, 
under  thick  beds  of  consolidated  butf  and  grey  sand  with  pebbles 
disseminated  through  the  lower  parts. 

j.  Dr.  Paris  (T.  E.  G.  S.  Corn.  vol.  i.  p.  7)  noticed  a  mass  of  sand 
near  Godrevy  Island,  containing  whole  shells  and  slate  fragments, 
12  to  20  feet  thick,  and  100  feet  in  length. 

k.  Dr.  Boase  _(T.  K.  G.  S.  Corn.  vol.  iv.  p.  469)  described  a  bed  of 
pebbles  above  high  water,  at  Godrevy  Point  and  around  Fistral  Bay, 
overlain  by  a  bed  of  testaceous  sand  ;  under  "  transported  but  un- 
altered debris,"  in  one  place  (op.  cit.  p.  309)  described  as  20  feet  of 
ferruginous  clay  with  angular  fragments  (local),  thinning  out  land- 
wards as  the  ground  rises. 

I.  Mr.  Whitley  (Journ.  E.  Inst.  Corn.  No.  11,  p.  184)  gives  a  sec- 
tion of  the  cliffs  under  Godrevy  Farm  from  top  to  base. 

Brown  loam  soil        Gin.  to  1  Sin. 

Clay  and  loam  with  numerous  angular  fragments  of  quartz...     6ft.  to  16ft. 
Sandy  loam  mixed  with  siliceous  sand,  and  portions  of  a  bed 

of  contorted  slate   (beheved  by  Mr.  Whitley  to  have  been 

pressed  into  the  bed  by  ice) 

Eed  and  white  siliceous  sand,  of  quartz  grains  partially  rounded. 
Boulders  of  blue  grit,  granite,  quartz,  vesicular  trap  (as  at 

St.  Minver). 
Slate  and  a  few  worn  flints  in  sand  cemented  by  the  oxides 

of  iron  and  manganese. 

m.  De  la  Beche  notices  (Eeport,  p.  426)  the  old  dunes  of  consoli- 
dated sand,  between  Gwythian  and  Godrevy  Head,  which  he  distin- 
guished from  the  underlying  raised  beach. 

17.  Observations  of  the  Fistral  Bay  Cliffs  made  here  and  there 
proceeding  northward. 

a.  South  end  of  the  Bay  (section  obscured  in  places).  Coarse  brown 
semi-consolidated  sand,  with  planes  resembling  bedding  and  false 
bedding,  containing  occasional  lines  of  small  angular  slate  and  quartz 
fragments,  20  feet  thick,  seems  to  underlie  Head,  shown  in  a  reced- 
ing part  of  the  cliff.  At  the  base  of  this  old  blown  sand,  a  trace  of 
blackish  coarse  consolidated  sand,  binding  pebbles  of  slate  and  quartz, 
is  visible  at  from  4  to  5  feet  aljove  high  water. 

h.  The  basement  beds  consist  of  gravel  of  small  quartz  pebbles, 
with  fair-sized  quartz  and  slate  pebbles,  and  large  subangular  slate 
fragments  in  blackish  sand,  1  foot  to  18  inches  thick ;  with  few  peb- 
bles and  of  a  brick-red  colour  in  places  ;  overlain  by  fine  blackish  and 
reddish  brown  sand  with  a  few  jjebbles  through  it,  from  2  to  3  feet 
in  thickness. 

c.  The  basement  beds  are  represented  by  two  beds  of  small  quartz 
and  slate  pebbles  and  subangular  stones,  6  inches,  and  from  6  inches 
to  a  foot  thick,  respectively,  separated  by  18  inches  of  coarse  blackish 
sand. 

d.  Coarse  consolidated  sand  of  slate  and  quartz  and  comminuted 
shells  rests  on  a  pebble  bed  2  feet  thick,  and  at  base  5  feet  above 
high  water.  The  pebbles  are  of  slate,  quartz,  and  occasionally  flint ; 
quartz  predominates ;  the  matrix  is  coai-se  grey  sand. 


W.  A.  E.  Ussher — Pod-Tertiary  Geology  of  Cornwall.       35 
e.  Cliff-section  toward  the  north  of  the  Bay — 


3ft. 

Oin. 

2ft. 

Oin. 

2ft. 

Oin. 

1ft. 

Oin. 

blown  sand    

Sandy  soil  with  angular  fragments  of  slate 

Buff  loam  with  angular  stones  and  boulders 

Buff  sand 

Coarse  and  fine  gravel  of  quartz,  dark  grey  grit,  slate  and, 

occasionally,  flint 4ft.     Oin. 

/.  Near  the  above  old  blown  sand  is  shown,  consisting  of  brown 
consolidated  sand  in  laminae  about  one-eighth  of  an  inch  thick,  con- 
taining pebbles  for  4  feet  upwards  from  its  base,  which  is  about  10 
feet  above  high  water. 

g.  About  100  yards  from  the  above  a  trace  of  consolidated  sand 
binds  pebbles  at  about  a  foot  above  high  water.  Old  consolidated 
blown  sand  is  shown  in  the  cliff  above ;  overlain  by  Head,  capped 
by  recent  blown  sand.  Two  whole  shells  of  Patella  were  found 
near  the  base  of  the  old  blown  sand,  which  forms  a  tough  bedded 
rock,  hardening  on  exposure  to  the  weather. 

Ti.  Dr.  Paris  (T.  E.  Gr.  S.  Com.  vol.  i.  p.  7)  described  the  old  beaches 
of  Fistral  Bay  and  New  Quay  as  a  horizontal  bed  of  pebbles,  10  to 
12  feet  thick,  containing  whole  shells  and  slate  fragments  cemented  in 
sand,  resting  on  slates,  and  supporting  immense  heaps  of  drifted  sand. 

i.  De  la  Beche  (Report,  p.  427)  describes  the  Fistral  raised  beach  as 
rolled  pebbles,  often  large,  mixed  with  smaller  gravel  and  sand, 
overlain  by  alternations  of  fine  gravel  and  sand  (the  layers  being 
unequally  consolidated),  capped  by  sand,  becoming  mingled  with 
rock  fragments,  near  the  extremity  of  the  dunes  on  the  north  and 
south. 

j.  Mr.  Pattison  (T.  R.  G.  S.  Corn.  vol.  vii.  p.  50)  mentions  the  inter- 
section of  the  Fistral  raised  beach  by  a  lead  lode,  in  the  middle  of 
the  Bay.  He  describes  the  present  beach  as  "  fine  sand  and  an 
abundance  of  shells ;  it  exhibits  no  pebbles  save  those  derived  from 
the  ancient  beach." 

18.  New  Quay. 

a.  On  the  east  side  of  Towan  Head,  a  trace  of  black  consolidated 
sand  with  pebbles  is  visible  at  about  6  feet  above  high  water. 

h.  On  the  west  of  New  Quay  Pier,  the  section  consists  of  coarse 
yellowish-brown  consolidated  sand,  chiefly  made  up  of  comminuted 
shells,  with  a  few  shells  of  Eelix ;  containing  angular,  subangular, 
and  rounded  stones  and  boulders  of  quartz  and  slate  (a  granitoid 
fragment  was  found)  at  the  base  ;  upon  coarser  sand  with  well- 
rounded  fragments  resting  on  a  narrow  rocky  platform  6  feet  above 
high-water  mark. 

c.  Dr.  Boase  (T.  R.  G.  S.  Corn.  vol.  iv.  p.  259)  ncjticed  a  bed  of 
shelly  sandstone,  on  the  north  of  New  Quay  signal  station,  contain- 
ing fewer  shells  than  at  Fistral  Bay  ;  the  lower  part,  just  above  high- 
water  mark,  being  consolidated  into  a  conglomerate. 

d.  De  la  Beche  (Report,  p.  427)  gives  a  section  on  the  east  of 
Look-Out  Hill,  New  Quay,  of  an  ancient  beach  of  rounded  slate 
pebbles  agglutinated  by  consolidated  sand,  some  feet  above  the  sea- 
level  ;    capped  by  layers  of  sand  of  comminuted  sea-shells  con- 


36       TF.  A.  E.  Ussher— Post-Tertiary  Geology  of  Cormcall 

solidated  in  the  lower  parts ;  under  a  Head  of  angular  fragments 
from  the  rocks  of  the  hill  above. 

19.  Between  New  Quay  and  Padstow. 

a.  A  thin  capping  of  Head  visible  on  part  of  Trevelga  Head  Island. 

h.  To  the  west  of  Tregurrian,  Head  of  angular  and  subangular 

slate  and  quartz  stones  is  shown  in  the  cliifs,  under  greyish  sandy  soil. 

c.  West  of  Trenance  (N.  of  Mawgan  Forth)  the  Head  consists  of 
brown  loamy  clay  with  large  quartz  boulders,  and  small  slate  and 
grit  stones. 

d.  At  the  north  end  of  Treyarnon  Bay  the  low  cliffs  are  capped 
by  G  inches  of  angular  quartz  and  slate  stones,  under  brown  clay, 
one  foot  thick. 

e.  The  cliffs  bounding  Constantine  Bay,  for  about  three-quarters 
of  a  mile,  seldom  exceed  7  feet  in  height.  Opposite  Constantine 
Island  the  cliff  is  composed  of — 

Blown  sand  with  a  layer  of  broken  Mijtili,  and  whole  Tatell(P; 
finer  in  the  lower  part,  and  containing  angular  pieces  of 

slate,  and  fragments  of  shells,  as  ahove      4  ft.     6in. 

upon — coarse  quartzose  sand  with  rounded  grains      1ft.  to  2it. 

resting  on  slates  at  6  feet  above  high  Avater. 

/.  Near  the  centre  of  Perleze  Bay  a  few  quartz  and  slate  pebbles, 
are  present,  under  blown  sand,  at  about  five  feet  above  high  water. 
g.  The  cliffs  of  the  cove  north  of  Trevone  (2  miles  west  of  Pad- 
stow)  are  from  5  to  15  feet  higli,  and  occasionally  capped  by  coarse 
brownish  sand,  giving  place  to  dark  brown  clay  with  angular  slate 
fragments  and  an  occasional  quartz  pebble.  The  ground  slopes 
upward  for  a  quarter  of  a  mile  very  gradually. 

20.  Between  Padstow  and  Tintagel. 

a.  On  the  cliffs  of  Bray  Hill,  near  St.  Enodock,  j'ellowish  and 
grey,  thin  bedded,  consolidated  sand  of  comminuted  shells,  con- 
taining shells  of  Helices,  is  visible  ;  at  base  5  feet  above  high  water. 

b.  In  one  place  the  following  section  occurs  under  2  feet  of 
recent  blown  sand : 

Consolidated  sand     6in. 

Dark  brown  loam,  containing  angular  fragments  of  quartz, 

slate  and  grit        " 2ft.  to  3ft. 

Upon  greenish  grey  slates  with  quartz  veins. 

c.  Near  the  mouth  of  the  St.  Enodock  Valley,  a  bed  of  consolidated 
sand,  one  foot  thick,  containing  land  shells  and  angular  fragments 
of  slate,  is  capped  by  recent  blown  sand,  and  rests  on  red  and  green 
banded  slates  at  8  feet  above  the  present  beach. 

d.  At  the  stream  mouth  between  Porteath  and  Trefan  Head, 
Head,  of  angular  stones  in  brown  and  yellowish  loam,  has  a  stratified 
appearance  in  the  distance,  owing  to  the  sizes  and  dispersion  of  the 
fragments  and  their  partial  absence  in  places.  The  stream  has  cut 
a  steep  bank  at  the  mouth  of  its  gorge,  which  exposes  20  feet  of 
Head — brown  loam  with  angular  slate  and  quartz  stones,  roughly 
horizontal  in  arrangement. 

e.  By  the  mouth  of  the  stream  west  of  Port  Isaac,  between 
Eoscarrock  and  Lobber  Kock,  20  feet  of  Head  is  shown,  consisting 
of  angular  fragments  of  slate  and  quartz  in  brown  loam. 


W.  A.  E.  Ussher — Post- Tertiary  Geology  of  Cormvall.        37 

/.  Near  Chapel  Eock  the  slates  have  been  cut  into  reef  platforms 
or  shelves,  in  places,  at  about  high-water  level. 

g.  At  the  mouth  of  the  stream  gorge  west  of  Dannon  Chapel,  10 
feet  of  Head  is  shown,  consisting  of  brown  loam  with  angular  slate 
and  quartz  stones. 

21.  The  Scilly  Isles. 

Mr.  Came  (Trans.  R.  G.  S.  Corn.  vol.  vii.  p.  140)  mentions  the 
occurrence  of  redistributed  granitic  matter,  called  "  secondary 
granite,"  on  Rat  Island,  at  Piper's  Hole  in  Tresco,  and  Piper's 
Hole  in  St.  Mary ;  in  both  the  latter  caverns  it  forms  the  principal 
part  of  the  roof,  and  contains  boulders  or  rounded  masses  of 
perfect  granite,  some  rather  large. 

Gknekal  Conclusions. 

Head. — The  position  of  the  stony  loam  or  Head  in  sites  where  no 
modern  talus  could  rest ;  the  denudation  it  has  undergone,  and  its 
frequent  presence  on  the  cliffs ;  prove  its  accumulation  to  have 
taken  place  subsequent  to  the  formation  of  the  raised  beaches,  yet 
considerably  anterior  to  the  prevalence  of  the  present  climatal  con- 
ditions. It  marks,  as  Mr.  Godwin-Austen  (Q.J.G.S.  vol.  vii.  p.  122) 
says,  "  A  time  when  the  degradation  of  the  surface  proceeded  much 
more  rapidly,  and  when  fragments  of  rock  far  exceeding  the  motive 
power  of  any  rainfall  were  conveyed  down  sloj^es  along  which  only 
the  minutest  particles  of  matter  are  now  carried"  {vide  9  c).  Such 
conditions  of  long-continued  subaerial  waste  are  likely  to  have 
prevailed,  as  Mr.  Godwin-Austen  suggests  (Q.J.G.S.  vol.  vi.  p.  93, 
etc.),  during  a  greater  elevation  of  the  (South)  West  of  England. 

The  rough  appearance  of  stratification  sometimes  noticeable  in  the 
Head  [(1)  through  the  horizontal  lie  and  apparent  regard  to  gravity 
in  distribution  of  its  contained  fragments,  vide  oh;  5b;  13  a;  20  d; 
(2)  through  strips  of  loam  or  clay  without  stones,  as  in  the  higher 
cliffs  bordering  Pra  Sands,  and  15  h ;  (3)  through  percolation  of 
water  carrying  down  overlying  substances  to  a  certain  horizon,  as 
17  e ;  (4)  through  distribution  of  colouring  matter,  as  5  b,  13  a]  may 
in  many  cases  be  due  to  fluviatile  deposition,  to  which  Mr.  Godwin- 
Austen  referred  the  Head  at  Swanpool  (5  d)  and  other  places. 

We  cannot  suppose  that  no  fluviatile  deposits  were  formed  during 
this  period  of  subaerial  waste ;  judging  from  the  pell-mell  distribu- 
tion of  angular  fragments  in  the  torrential  gravels  of  the  present 
streams,  in  their  higher  reaches,  it  is  only  reasonable  to  expect  that 
similar  deposition  would  then  have  taken  place  on  a  much  larger 
scale,  and  that  its  traces  would  be  found  in  the  present  area  of  the 
county  which  would  only  represent  the  highlands  of  its  former 
extension. 

Raised  Beaches. — The  general  consolidation  of  the  old  beach  mate- 
rials, occasionally  into  a  very  hard  rock  {vide  6c;  16  ^,  ^;  18),  renders 
their  detection,  even  as  fragments  on  a  level  with  the  surface  of  the 
present  beach,  comparatively  easy ;  where,  however,  the  process  of 
consolidation  was  interfered  with  by  the  accumulation  of  the  Head. 


38        W.  A.  E.  JJssher — Post-Tertiary  Geology  of  Cormcall. 

the  beach  material  seems  to  have  been  swept  away,  and  in  some 
cases  to  have  left  traces  in  occasional  pebbles  at  or  near  the  base  of 
the  Head  {vide  5  a;  6a;  16  a;  and  perhaps  19 g).  Even  where  the 
raised  beach  is  well  developed,  the  upper  part  has  been  sometimes 
mingled  with  the  base  of  the  overlying  talus  (13  b).  Angular  frag- 
ments are  occasionally  found  in  the  raised  beaches  (16/).  The 
above  observations  serve  to  explain  the  aj^pearance  of  beach  material 
on  Head,  S.  of  Perranuthno  (9  g),  as,  in  an  adjacent  section  (9  g'), 
the  Head  is  represented  by  pebljles  and  subangular  fragments.  On 
Bray  Hill  (20  b),  6  inches  of  consolidated  sand  rests  on  2  to  3  feet  of 
Head ;  but  the  latter  is  represented  in  an  adjacent  spot  by  con- 
solidated sand  with  angular  fragments  of  slate,  and  land  shells  (20  c) ; 
so  that  the  old  sand  drift  may  have  taken  place  on  the  beach  plat- 
form after  a  little  talus  had  been  shed  upon  it  during  the  earliest 
symptoms  of  elevation. 

It  is  often  diificult,  where  old  consolidated  blown  sands  occur,  to 
distinguish  their  junction  with  underlying  raised  beaches,  as  pebbles 
and  fragments  of  Mytili,  Patellce,  etc.  (16  «;  17  f,  g ;  18)  may 
have  been  cast  upon  the  dunes  by  storm  waves ;  their  presence  and 
linear  ari'angement  in  recent  blown  sand  (19  e)  would  seem  to  be 
due  to  protracted  gales  from  the  same  quarter. 

Being  chiefly  composed  of  comminuted  shells,  the  percolation  of 
water  through  the  old  dunes  would  best  explain  their  consolidation. 
Dr.  Paris  (T.R.G.S.  Corn.  vol.  i.  p.  7),  in  addition  to  this,  gives  two 
other  possible  modes  of  consolidation,  viz..  by  water  charged  with 
pyritical  substances,  or  by  ferruginous  infiltration. 

The  absence  of  organic  remains  in  the  majority  of  the  Cornish 
raised  beaches  has  been  ascribed  to  Arctic  currents  (God win- Austen, 
Q.J.G.S.  vol.  vi.  p.  87),  which  I  think  very  probable.  It  also 
suggests  the  possibility  that  many  of  them  may  have  been  deposited 
by  rivers,  or  in  estuaries,  whose  seaward  banks  have  been  swept 
away.  Some  of  the  boulder  beds  mentioned  by  Messrs.  Carne  and 
Henwood  are  at  too  great  heights  to  be  regarded  as  raised  beaches, 
and  may  more  reasonably  be  referred  to  far  older  fluviatile  deposi- 
tion, if  the  adit  mentioned  by  Mr.  Henwood  (12  b)  cut  tlirough 
a  continuation  of  the  worn  boulder  beds  of  Porth  Just  and 
Pornanvon  to  a  thickness  of  60  feet,  the  boulder  beaches  of  these 
localities  must  be  regarded  as  anterior  to  the  raised  beaches.  In  the 
formation  of  the  old  beach  cliffs  at  the  termination  of  a  long  period 
of  subsidence,  fluviatile  deposits  (thrown  down  before,  and  during, 
the  initiation  of  the  present  lines  of  drainage)  would  have  been 
truncated,  so  to  speak,  and  exposed  at  different  heights  upon  the 
cliffs,  just  as  we  find  old  river  gravels  exposed  on  the  secondary 
cliil'-line  of  Devon. 

Again,  during  the  elevation  of  the  old  beaches,  the  existing  river 
channels  would  have  been  deepened,  and  river  deposits  formed  in 
the  breaches  of  the  old  cliff-line,  to  be  redistributed  by  the  sea  in 
its  recent  advance.  How  far  boulder  gravels  and  unfossiliferous 
raised  beaches  (provisionally  so  called)  may  be  referred  to  either  of 
these  periods  of  fluviatile  action  it  is  impossible  to  say,  without  a 


W.  A.  E.  JJssher — Post-  Tertiary  Geology  of  Cornwall.       39 

searching  investigation  of  each  particular  deposit  with  reference  to 
its  surroundings. 

The  local  elevation  of  the  raised  beaches  cannot  be  correctly 
measured  by  the  height  above  high  water  of  their  remains ;  for 
such  an  estimate  ignores  the  original  thickness  of  the  beaches,  and 
postulates  an  identity  in  the  local  rise  of  tide  during  the  raised 
beach  formation  and  at  present.  The  latter  supposition  is  im- 
probable when  we  take  into  account — 

Istly.  The  destruction  by  the  sea,  during  elevation  (of  the  old 
beaches),  of  such  inequalities  as  may  have  proved  obstacles  to  the 
stream  of  tide. 

2ndly.  The  modification  the  raised  sea-bed  would  have  undergone 
through  subaerial  agencies. 

Srdly.  The  probably  different  relations  of  land  and  sea  in  other 
parts  of  England,  and  on  neighbouring  coasts  during  the  formation 
of  raised  beaches  in  the  S.W.  counties. 

4thly.  The  subsequent  modification  of  the  old  coast-line. 

Mr.  Pengelly  (Trans.  Dev.  Assoc,  part  v.  p.  103)  points  out  the 
fallacy  of  supposing — that  all  contemporary  raised  beaches  are  on 
the  same  level,  and  the  converse — that  raised  beaches  on  the  same 
level  are  necessarily  contemporaneous.  The  cautions  given  show 
the  danger  of  laying  stress  upon  individual  observations  which 
may  be  taken  where  the  beach  was  left  very  thin,  or  at  different 
parts  of  its  seaward  slope. 

The  base  of  the  Cornish  raised  beaches  above  high- water  is  shown 
by  observations  to  average  5  feet ;  such  cases  as  Pendeen  Cove 
(14)  ;  Tremearne  (9  V)  ;  Nanjulian  (11  c)  ;  Forth  Just  (12  a) ;  being 
exceptional.  Taking  the  thickness  of  the  old  beaches  at  15  feet  as  a 
maximum,  the  average  subsidence  indicated  by  them  would  be  from 
12  to  20  feet  below  high  water. 

De  la  Beche  (Geological  Manual,  p.  157)  gives  a  section  of  the 
successive  faces  (indicated  by  dotted  lines)  that  the  degradation  of  a 
cliff  composed  of  Head  upon  raised  beach  would  be  likely  to  exhibit 
(see  Fig.  6). 


Sea-level.   /?  5/  ^  \^//////t///////////////////fi///f///fm////r''llill'///^    Sea-level 


Fig.  6. — H,  Head,  concealing  a  raised  beach,  resting  upon  slate,  S,  above  the 
sea-level. 

The  raised  beach  platform  has  been  cut  too  far  back  to  allow 
of  such  cliff  faces  as  1  and  2.  Exceptions  to  this  rule  may  be 
furnished  by  the  low  tract  at  Spit  Point  near  Par ;  the  lowlands  of 
St.  Keverne  (7  c) ;  the  flattish  tract  covered  by  blown  sand  between 
Constantine  and  Perleze  Bays,  if  the  waterworn  sand  (in  19  e)  is  a 


40        W.  A.  E.  Ussher — Post-Terfianj  Geology  of  Cornwall. 

trace  of  raised  beach,  or  rests  on  an  old  beach  platform  ;  the  gently 
sloping  tract  bordering  the  coast  near  Trevone  (19  g). 

The  cliffs  bordering  a  part  of  Pra  Sands  are  wholly  composed 
of  Head  to  a  height  of  60  feet  from  the  present  beach  ;  Ijut  as  Head 
rests  on  a  portion  of  raised  beach  on  an  adjacent  promontory,  on  a 
platform  5  feet  above  high  water,^  the  old  beach  platform  may  in 
this  instance  have  been  broken  up  by  fluviatile  agencies  prior  to  or 
during  the  accumulation  of  the  Head ;  or  the  original  surface  of  the 
platform  must  have  been  most  irregular.  Such  cliffs  as  Nos.  3  and  i 
are  by  far  the  most  general  sections  on  the  Cornish  coast,  which  has 
been  in  very  many  places  cut  too  far  back  to  show  either  raised  beach 
or  Head. 


PART    IV. 

PLEISTOCENE    GEOLOGY    OF    COJEiN^WA.lL.T.. 

Submerged  Forests  and  Stream  Tin  Gravels. 

THE  evidence  under  this  head  is  necessarily  a  compilation ;  the 
very  exceptional  exposure  of  the  old  forest  ground,  and  the 
nature  of  stream  tin  sections,  leaving  no  room  for  personal  investi- 
gation. The  names  of  the  observers  are  in  most  cases  sufficient 
vouchers  for  the  accuracy  of  their  statements.  The  submerged 
forests  are  given  first,  as  there  is  no  evidence  forthcoming  to  show 
the  priority  of  the  sti'eam  tin  gravels  to  the  general  growth  of  the 
forests.  The  forest  bed  overlying  the  stream  tin  which  Mr.  Carne 
rightly  synchronizes  with  the  forest  beds  on  the  coast  may  represent 
a  very  brief  portion  of  a  long  period  of  forestial  growth. 

Submerged  Forests. — Proceeding  round  the  coasts  from  Plymouth. 

1.  Looe.  Mr.  Box  (2Gth  Ann.  Eep.  Pioyal  Inst.  Corn,  for  18U) 
noticed  trunks  of  oak,  alder,  ash,  and  elm,  on  Millendreath  Beach, 
in  vegetable  mould  extending  for  250  yards  from  east  to  west,  and 
sloping  from  below  high-water  mark  to  the  southward  for  150  feet, 
where  it  was  lost  sight  of  under  fine  sand,  which,  though  explored 
for  30  feet  farther  out,  yielded  no  further  traces.  The  plants  in  the 
mould  resembled  those  foimd  in  a  neighbouring  marsh,  130  feet 
above  high  watex',  of  which  the  following  section  is  given  : — 

Peat  of  flags  and  anmdaceous  plants. 

■Dark  brown  vegetable  matter  with  holly  and  alder. 

Layer  of  sand  with  vegetable  matter,  numerous  hazel  nuts,  and  the  elj'tra 
of  Coleopterous  insects,  also  black  oak  and  h  holly,  resting  on  firm  light- 
coloured  clay. 


W.  A.  E.  JJssher — Pleistocene  Geology  of  Cornwall.        41 

Numerous  angular  slate  fragments  were  met  witli,  but  no  shells. 

2.  Near  Mevagissey.  Sir  C.  Lemon  (T.  K.  Gr.  S.  Corn.  vol.  vii.  p. 
29)  gives  the  following  section  disclosed  in  cutting  a  drain  at  Heli- 
gan  (about  a  mile  inland  from  Mevagissey  Bay)  near  the  foot  of  a 
hill  20  feet  above  the  stream  in  the  valley  bottom,  and  in  another 
place,  higher  up,  at  40  feet  above  the  stream  : — Loam  1  foot  8  inches 
fi'om  the  surface,  upon  a  mass  of  whitish,  bluish,  and  yellowish  clay 
with  broken  slate,  with  the  stump  of  an  oak  4  feet  long  and  nearly 
a  foot  in  diameter,  7  feet  4  inches  from  the  surface  at  its  lower 
extremity. 

Submerged  forests  have  been  observed  after  severe  gales — 

3.  At  Fowey  by  Mr.  Peach  (T.  E.  G.  S.  Corn.  vol.  vii.  p.  62),  the 
trees  being  rooted  in  stiff  clay. 

4.  At  Porthmellin,  near  Mevagissey  {Jh'id,  vol.  vi.  pp.  23  and  51), 
the  roots  resting  on  clay  apparently  in  situ. 

5.  At  Maen  Forth,  near  Falmouth,  by  the  Kev.  J.  Kogers  (Ibid, 
vol.  iv.  p.  481),  the  "roots  being  in  clay. 

6.  At  Porthleven  near  the  Loo  Pool,  by  the  Eev.  J.  Rogers  {Ibid, 
vol.  i.  p.  236),  oak  and  willow  roots  apparently  in  situ.  At  Fowey 
and  Porthmellin,  elytra  of  beetles  were  found. 

7.  Mr.  H.  M.  Whitley  (Journ.  E.  Inst.  Corn.  No.  13,  p.  77)  gives 
the  following  section  at  Market  Strand,  Falmouth,  exposed  during 
excavations  at  the  Landing  Pier : — 

Layer  of  sand  on  a  thin  bed  of  shale,  thinning  out  seaward    ...     2ft.     Oin. 
on— Forest  Bed,  compact  peat,  flags,  ferns,  trees  of  oak,  hazel, 
fir,  beech  ;  fir  and  beech  most  abundant ;  no  hazel  nuts  obtained     7ft.     Oin. 
The  top  of  this  bed  occurred  at  about  the  level  of  ordinary 
spring-tide  low-water  mark.     Its  base  rested  on  a  layer  of 
gravel         4ft.     Oin. 

Mr.  Whitley  was  informed  that  the  forest  bed  extended  for  a  short 
distance  up  the  valley,  and  that  another  part  of  it  had  been  met  with 
in  an  excavation  at  Bar  Pools.  The  open  space  before  the  market  is 
called  "  the  Moor." 

.  8  «.  Mounts  Bay.  Leland  thus  alhides  to  the  submerged  forest 
in  Mounts  Bay — "  In  the  Bay  betwyxt  the  Mont  and  Pensants  be 
found  near  the  lowe  water  marke  Eoots  of  Trees  yn  dy vers  places  as 
a  token  of  the  ground  wasted." 

b.  Dr.  Borlase  (Trans.  Eoy.  Soc.  for  1757,  p.  80)  noted  the  dis- 
covery of  roots,  trunks,  and  branches  of  oak,  hazel,  and  willow,  on 
the  shores  of  Mounts  Bay,  in  black  marsh  earth  with  leaves  of 
Juncus,  under  10  feet  of  sand. 

c.  Dr.  Boase  (T.  R.  G.  S.  Corn.  vol.  iii.  p.  131)  mentioned  the  oc- 
currence of  vegetable  mould  with  roots  and  trunks  of  indigenous 
trees,  under  2  to  3  feet  of  sand  on  the  west  of  St.  Michael's  Mount. 

d.  Mr.  Carne  (T.  E.  G.  S.  Corn.  vol.  vi.  p.  230)  noticed  the  occur- 
rence of  trees  on  peat,  east  of  Penzance,  the  largest  being  an  oak 
trunk  with  bark  on,  6  feet  long  and  1^  feet  in  diameter. 

e.  He  also  mentioned  the  occurrence  of  a  peat  bed  3  to  8  feet 
thick  in  the  low  tract  between  Marazion  and  Ludgvan  (a  reclaimed 
marsh) ;  it  extends  for  2  miles,  from  a  little  eastward  of  Chyandour 


42        W.  A.  E.  Ussher — Pleistocene  Geology  of  Cormcall. 

to  the  Marazion  River.  Near  Longbridge,  where  it  approaches  the 
surface,  it  is  from  4  to  7  feet  thick,  and  used  for  fuel ;  it  rests  on  a 
thick  bed  containing  Cardiiim  edule,  and  is  generally  concealed  by 
alluvium. 

9.  Mr.  Henwood  (40th  Annual  Rep.  R.  Inst.  Corn,  for  1858) 
describes  a  submarine  forest  on  Dunbar  Sands  in  the  Camel  Estuary. 
Nothing  save  spongy  masses  of  peaty  sand  were  visible  in  1875,  when 
I  visited  the  spot,  the  roots,  etc.,  having  been  probably  washed  away 
in  the  interim. 

10.  De  la  Beche  says  that  traces  of  submarine  forests  were  noticed 
at  Perran  Forth,  Lower  St.  Columb  Forth,  and  Mawgan  Forth. 
(Report,  p.  419).  No  signs  of  them  were  visible  on  the  occasion  of 
my  visit.  St.  Columb  Forth  is  a  sand  flat,  at  low  water,  between 
cliffs  not  10  feet  in  height,  exhibiting  no  traces  of  old  marine  action. 
Mawgan  Forth  is  a  similar  sand  flat,  but  broader,  and  terminating  in 
low  sand  dunes,  to  the  south  of  which  narrow  strips  of  alluvium 
border  the  streams. 

11.  Bude.  Mr.  S.  R.  Fattison  (T.  R.  G.  S.  Corn.  vol.  vii.  p.  35) 
noticed  roots  of  trees  of  large  size,  apparently  in  situ,  in  dark  clay,  at 
Maev  Lake,  near  Bude  Haven. 

12.  ilr.  Fattison  also  noticed  large  accumulations  of  bog  timber 
in  the  Fowey  Vallej'^  on  Bodmin  Moor.  At  Bolventor  the  heads  of 
the  trees  pointed  down  the  valle}'. 

Stream  Tin  Sections. 

1.  De  la  Beche  (Report,  p.  405)  says  that  in  the  interior  the  tin 
ground  is  usually  covered  by  river  detritus,  more  open  spaces  fre- 
quently having  a  bed  of  peat  (in  which  oaks  are  common)  interposed 
between  the  tin  ground  and  other  detrital  accumulations,  as  in 
Tregoss  Moor  and  the  moors  adjacent  to  Hensborough.  "  In  some 
whole  gi'ound  (stream  tinners'  term  for  stannifei'ous  gravel)  and 
superincumbent  beds  not  previously  disturbed  by  the  old  men,  upon 
Bodmin  Const  Moor,  the  peat  beds  with  oak,  alder,  etc.,  covering 
the  tin  ground  very  irregularly,  were  in  some  places  several  feet 
thick,  in  others  absent,  though  on  the  whole  they  seemed  to  keep  a 
somewhat  common  level  above  the  tin  ground.  In  some  places  thin 
peat  beds  had  been  accumulated  at  still  higher  levels  among  the 
gravels,  sands,  and  clays.  The  shelf  composed  of  semi-decomposed 
granite  was  very  irregular,  holes  30  or  40  feet  deep  presenting 
themselves,  in  the  bottoms  of  which  there  was  usually  good  stanni- 
ferous gravel." 

2.  Mr.  Fattison  (op.  cit.)  gives  a  section  of  the  Fowey  Valley  Works, 
in  which  the  (hard  and  l^lack)  forest  bed  was  met  with  at  from 
23  to  27  feet  below  the  surface,  resting  on  stream  tin  gravel,  and 
overlain  by  sand  with  a  peat  bed  containing  ferns  and  hazel. 
The  granite  shelf,  tin  gravel,  and  forest  bed  presented  a  faulted 
appearance. 

3.  Far.  De  la  Beche  (Report,  p.  403).  In  cutting  the  Par  Canal 
at  Pons  Mill,  near  St.  Blazey,  granite  blocks,  as  if  arranged  for  a 
bridge,   were  found   beneath  20    feet  of  gravel,   probably  in  part 


W.  A.  E.  Ussher — Pleistocene  Geology  of  Cornwall.        43 

resulting  from  stream  tin  washing.     Section  in  low  ground  near  the 
Par  Estuary — 

1.  River  deposits 1ft.     6in. 

2  and  3.  Mud,  sand,  clay,  stones,  much  disturbed  by  the 
stream   tinners    in    the    upper  part;  with  vegetable 

matter  in  the  lower  part     15ft.     Oin. 

4.  Fine  sand  with  sea    shells  like  cockles,   and   rolled 

pebbles  in  the  upper  part 4ft.     Oin. 

6.  Mud,  clay,  sand,  wood,  nuts,  etc.,  mixed       3ft.     Oin. 

6.  Tin  ground  resting  upon  an  uneven  siu'face  of  slate    ...    6in.  to  6ft.     Oin. 
4.  North   of  St.    Austell.     Mr.    Henwood   gives    the    following 
sections.     The  letters  prefixed  denoting  beds  probably  contempor- 
aneous.    (T.K.G.S.  Corn.  voL  iv.  pp.  60  to  64.) 

A.  Merry  Meeting,  in  parish  of  St.  Koche. 

a.  Mud,  with  decayed  vegetable  matter       2ft.  to  3ft. 

1.  Granitic  gravel ...  2ft. 

2.  Silt,  with  decayed  vegetable  matter  and  plates  of  mica     ...     4ft.  to  5ft. 

b.  Granitic  stones,  gravel  and  sand  mixed  with  silt  and  nuts    . . .  4ft. 

3.  Vegetable  matter   (locally   called  Fen),   moss,  grass,  wood 

(P  charred) 1ft. 

4.  Silt  (vegetable  remains  ?)  1ft. 

6.  Vegetable  remains  (charred  like  No.  3) 1ft.  to  3ft. 

6.  Vegetable  matter  passing  into  silt    Sin.  to  lOin. 

c.  Tin  ground,  with  enormous  quartz  blocks,  some  15  ft.  square  ; 

tin  ore  as  sand,  stones,  and  pebbles  mixed  with  quartz, 
granite,  and  schorl  rock;  little  rounded,  and  of  the  best 
quality  where  the  decomposed  granite  shelf  is  softest... 

B.  In  the  centre  of  Pendelow  Vale. 

a.  Granitic  sand  and  gravel  

1.  Silt  (vegetable  matter  P)    

2.  Granitic  sand      

3.  Vegetable  matter  (like  No.  5  in  other  sections,  but  with  sand) 

b.  Silt,  sand,  and  gravel  mixed     

4.  Vegetable  matter  (Hke  No.  5  in  other  sections)  (Fen) 
6.  Tin  groimd,  ore  not  abundant,  most  plentiful  near  the  base 

C  Watergate. 

a.  Mud  with  granitic  sand  and  gravel        

1.  Fine  granitic  sand     

2.  Silt  (with  decayed  vegetable  matter  ?)   ... 

3.  Fine  granitic  sand     

4.  Silt  (resembling  No.  2)    

b.  Silt,  sand,  gravel,  and  large  stones,  indiscriminately  mixed 

5.  Vegetable  matter  passing  into  silt  in  the  lower  part  (like 

Nos.  5  and  6  in  the  Merry  Meeting  section)      

C.Tin  ground;    the  ore  occurs  as  sand  and  pebbles 

D.  Broadwater,  Luxillion.  Tin  ore  much  larger  towards  the  sea 
than  up  the  vale.  A  patch  of  slate  some  hundreds  of  feet  in  area 
was  found  resting  on  tin  ground,  and  apparently  unconnected  with 
the  shelf. 

a.  Granitic  sand    6ft.  to  7ft.     Oin. 

b.  Mud,  apparently  of  vegetable  origin,  mixed  with  granitic 

sand  and  gravel     4ft.  to  5ft.     Oin. 

c.  Tin  ground;   ore,  small  pebbles  not  much  rounded     ...  7ft.     Oin. 

The  tin  bed  is  sometimes  divided  by  a  bed  of  granite  (cap  shelf) 
as  at  Grove  and  Merry  Meeting.  Numerous  blocks  of  quartz  lie  on, 
the  shelf.     Below  the  shelf  (soft  granite)  tin  ore  is  not  abundant. 


...   4ft.  to 

soft. 

...     12ft. 

Oin. 

...       1ft. 

Oin. 

...      4ft. 

Oin. 

and)      2ft. 

Oin. 

...       2ft. 

Oin. 

...      4ft. 

Oin. 

ase        5ft. 

Oin. 

6ft. 

Oin. 

2ft.  to  3ft. 

Oin. 

2ft. 

6in. 

2in.  to  Sin. 

3ft. 

Oin. 

3ft. 

Oin. 

5ft.  to  6ft. 

2ft.  to  20ft. 

lOft.  to  loft. 

Gin. 

1ft. 
5ft.  to    6ft. 

Oin. 
Oin. 

3ft.  to  10ft. 

Oin. 

Oft. 
1ft.  to  3ft. 

6  in. 
Oin. 

44        W.  A.  E.  Ussher — Pleistocene  Geology  of  Cornwall. 

The  following  are  from  Journ.  R.  Inst.  Corn.  vol.  iv.  p.  214  : — 

E.  Levrean  in  St.  Austell's  parish. 

1.  Granitic  sand  and  gravel     ...  Ift-     Oin. 

2.  Peat  (Fen),  often  mixed  with,  and  sometimes  divided 

by,  very  thin  layers  of  granitic  sand       1ft.     Oin. 

3.  Granitic  matter,  particles  and  granules  of  tin,  rarely 

mmute  specks  of  gold  (Upper  Tin  Ground)   ...     ...     3ft.  to       6ft.     Oin. 

4.  Angular  and  subangular  masses  of  granite  in  granitic 

sand  without  any  tin  ore  (False  Shelf) 1ft.  to  l-^jft.     Oin. 

5.  Tin  gi'ound;  angular  and  subangular  granite,  felspar, 

quartz,  schorl,  veinstone  materials  mixed  with 
granitic  gravel  and  sand,  grains  and  particles  of  tin 
oxide,  and  less  frequently  flakes  of  schistose  matter 
with  specks  of  gold.  A  few  ancient  shovels  of 
wood,  bound  on  the  edges  with  iron,  have  been 
found  in  this  bed.  The  shelf  is  of  granite  of 
unequal  hardness       

F.  Pit  Moor  in  St.  Austell's  Parish. 
1.  Vegetable  mould 

2  and  3.  Granitic  detritus  in  many  layers      

4.  Tin    ground;     angular,    subangular,    and    rounded 

masses  of  granite,  quartz,  schorl,  veinstones,  small 

quantities  of  tin  ore  ;  clay-slate  laminae,  occasional ; 

on  soft  granite  shelf 

G.  Upper  Creamy  (Wheal  Prosper). 

1.  Peat ... ...     . 

2.  Granitic  clay,  often  mixed  with  laminte  of  yellowish  slate 

3.  Tin  ground;    small  angular  and  rounded  granitic  and 

veinstone  material ;  tin  stone  as  sand  and  gravel ; 
microscopic  particles  of  gold.  On  shelf  of  bluish  and 
brownish  clay.  The  roots  of  marsh  plants  penetrate 
the  tin  ground       4ft.  to  5ft.     Oin. 

E.  N.W.  of  the  Railway  Bridge  over   the   high   road   between 
Lanivet  and  the  Indian  Queens. 

1.  Vegetable  mould      6in.  to  1ft. 

2.  Angular  and  subangular  stones  of  quartz,  slate,  elvan, 

schorl  rock,  slate  veinstones,  and  occasionally  granite  Sin.  to  4ft. 

3.  Tin   ground  like  the   overburden,  but  with   rounded 

masses  of  tin  ore,  often  ver)-  small ;   on  shelf  of  clay 

slate        1ft.  to  2ft. 

I.  Gun-deep  in  St.  Denis. 

1.  Vegetable  mould       6in.  to  1ft. 

2.  Gravel,  stones  of  slate,  quartz,  elvan,  schorl  rock,  and 

occasionally  granite      4ft. 

3.  Peat 1ft. 

On  4.  Tin  ground ;  poor. 

J.  On  N.  side  of  Tregoss  Moor.    Ancient  works  resumed  at  Golden 
Stream  about  half  a  miie  S.E.  of  Castle-an-dinas  in  St.  Columb  Major. 

1.  Vegetable  mould      Oft.     Gin. 

2.  Angular  and  subangular  masses  of  slate,  quartz,  elvan, 

schorl  rock,  veinstones,  and  occasionally  granite; 
lumps  of  peat  had  been  previously  removed  from  this 
bed 6ft.  to  6ft.    Oin. 

3.  Tin  ground  resembling  the  overburden,  but  with  more 

numerous  fi-agments  of  elvan ;   the  tin  ore  as  gravel 

or  sand 2ft.  to  3ft.     Oin. 


W.  A.  E.  Ussher — Pleistocene  Geology  of  Cornwall.        45 

K.  Dr.  Boase  (T.R.G.S.  Corn.  vol.  iv.  p.  248)  mentioned  the 
occurrence  of  siliceous  sand  under  diluvial  debris  in  the  Stream 
Works  near  Hensborough,  on  the  road  to  Eoche.  At  Tregoss  and 
Eoche  the  tin  ground  contained  quartz  and  schorl  pebbles,  and  the 
shelf  consists  of  decomposed  slaty  felspathic  rock. 

L.  Hen  wood  (J.E.  Inst.  Corn.  vol.  iv.  p.  230),  Section  at  Penny- 
Snap  (Wheal  Prosper,  in  Alternun)  E.  of  the  Drains  Eiver — 

1.  Peat 7ft.     Oin. 

2.  Angular  and  worn  granite,  elvan,  schorl,  and  quartz  stones 

in  pale  blue  felspathic  clay,  averaging        5ft.     Oin. 

3.  Tin  ground  as  above,  with  tin  ore  as  waterworn  sand  or 

gravel;    on  granite  shelf      3ft.     Oin. 

5  A.  The  section  of  the  Happy  Union  Works  by  Mr.  Colenso 
(1829)  has  been  quoted  by  several  writers,  but  by  none  more  fully 
than  De  la  Beche,  from  whom  I  extract  (Eeport,  pp.  401,  402,  403), 
giving  the  deposits  in  reverse  order. 

1.  Eough  river  sand  and  gravel,  here  and  there  mixed  with  sea 

sand  and  silt.  A  row  of  wooden  piles  with  their  tops  24 
feet  from  the  surface,  apparently  intended  for  a  bridge, 
were  found  on  a  level  with  spring-tide  low-water     20ft.     Oin. 

2.  Sand;  trees  all  through  it,  chiefly  oaks,  lying  in  all  directions; 

animal  remains,  bones  of  red  deer,  hog,  human  skulls  (?), 

bones  of  whales 20ft.    Oin. 

3.  Silt  or  clay  and  layers  of  stones,  a  conglomerate  of  sand, 

silt,  bones  and  wood     2ft.     Oin. 

4.  Sand  with  marine  shells ;    water  draining  through  this  bed 

is  salt  above,  fresh  below     Oft.     4in. 

5.  Sludge,  or  silt,  brownish  to  a  lead  colour  in  places,  with 

recent  shells  which,  particularly  the  bivalves,  are  often  in 
layers,  double  and  closed,  with  the  siphonal  end  upward, 
rendering  it  likely  that  they  lived  and  died  there ;  they 
are  of  the  same  species  as  those  existing  in  the  neighbour- 
ing sea  ;  wood,  hazel  nuts,  and  occasionally  bones  and  horns 
of  deer  and  oxen  are  found  in  this  bed :  a  piece  of  oak, 
shaped  as  if  by  man,  with  a  barnacle  attached,  was  found 
at  2  feet  fi-om  the  top 10ft.     Oin. 

6.  A  layer  of  leaves,  hazel  nuts,  sticks,  and  moss  (in  a  perfect 

state,  almost  retaining  its  natm-al  colour,  apparently  where 
it  grew).  It  extends,  with  some  interruptions,  across  the 
valley,  occurs  at  30  feet  below  low-water  mark,  and  about 
48  feet  below  spring-tide  high-water 6in.  to  12in. 

7.  Dark    silt,  apparently  mixed  with  decomposed  vegetable 

matter     1ft.     Oin. 

8.  Eoots  of  trees  in  their  natural  position;  oaks  with  fibres 

traceable  for  2  feet  deep.  "  From  the  manner  in  which 
they  spread  there  can  be  no  doubt  but  that  the  trees  have 
grown  and  fallen  on  the  spot  where  their  roots  are  found." 
Oyster-shells  still  remain  fastened  to  some  of  the  larger 
stones  and  to  the  stumps  of  trees 

9.  Tin  ground,  with  rounded  pieces  of  gi-anite,  and  subangular 

pieces  of  slate  and  greenstone.  Most  of  the  tin  occurs  in 
the  lower  part,  from  the  size  of  the  finest  sand  to  pebbles 
lOlbs.  in  weight;  some  rocks  richly  impregnated  with  tin 
weigh  2001bs.   and  upwards.     Thickness  (including  No. 

8)  from ...     ,.,     3ft.  to  10ft. 

B.  De  la  Beche  (Eeport,  p.  403)  says,  "These  works  are  now 
abandoned,"  others  on  S.  of  London  Apprentice  Inn  were  carried  on 
in  1837 :    "  from  which  it  would  appear  that  from  the  general  rise 


46         W.  A.  E.  JJssher — Pleistocene  Geology  of  Cornivall. 

of  its  bottom,  the  sea  had  not  entered  this  valley  suflSciently  high 
to  permit  marine  deposits  to  be  there  accumulated."  This  probably 
refers  to  Mr.  Colenso's  section  of  Wheal  Virgin  Works  (T.R.G.S. 
Corn.  vol.  iv.  p.  38),  a  mile  from  Happy  Union,  in  which  no  sea 
sand  was  found.  The  tin  ground  betraying  signs  of  old  men's 
workings  lay  beneath  32  feet  of  silt  and  river  gravel,  with  oak, 
willow,  etc.,  in  considerable  quantity,  with  their  roots  in  situ  where 
soil  exists.  "  How  far,"  says  Mr.  Colenso,  "  Pentuan  Valley  extended 
seawards  is  conjectural,  but  at  its  present  declivit}'  of  45  feet  to 
a  mile  between  St.  Austell  and  Pentuan,  it  must  have  continued 
a  mile  further  than  it  does  now."  Mr.  Smith  {Ibid,  p.  400) 
mentions  the  rapid  descent  of  the  valley  from  Hensborough  (900  to 
1000  feet  in  height),  and  the  continuance  of  a  bed  of  pebbles  all 
the  way. 

C.  Section  of  Lower  Pentewan  work,  quarter  of  a  mile  from  the 
beach  given  by  Mr.  Smith  (op.  cit.) — 

1.  Soil  with  growing  trees,  some  very  old;   gravelly  towards 

the  bottom         3-3 

2.  Fine  peat,  roots  of  trees,  fallen  trunks,  sticks,  ivy,  sea 

laver,  rushes,  impregnated  with  salt       ... 12-152 

3.  Sea  mud,  with  compressed  leaves  at  the  top,  cockles  at 

31  feet  from  the  surface,  bones,  human  skulls  (one  of  a 
child) ,  deer  horns.  At  the  bottom,  a  bed  of  very  small 
shells  a  foot  in  thickness 20-35 

4.  Sea  mud,  oysters,  and  cockles     4'39 

5.  Compressed  leaves,  vegetable  matter,  a  few  rotten  shells       6^"452 

6.  Vegetable  matter,  rushes,  fallen  trees,  leaves,  roots,  moss, 

the  wings  of  Coleopterous  insects    ...     .        r4fi| 

7.  Moss,  hazel  nuts,  sticks,  on  pebbles  of  killas,  growan,  etc.         3"49j 

8.  Rough  tin  ground,  stones  light  and  poor 2-51| 

9.  Eough  tin  ground,  rich  stones  with  quartz  pebbles  and 

yellow  ferruginous  clay.   Killas  at  about  low-water  mark        3'o4^ 

D.  (op.  cit.)  Section  of  Upper  Pentuan  works,  1  mile  N.  from  the 
beach,  where  the  valley  is  half  a  mile  wide. 

1.  Soil  with  trees  growing  on  it     3ft.       3in. 

2.  Mud  with  gravel  seams  resembling  false  bedding    21ft.     Uin. 

3  and  4.  Spar  and  killas  upon  growan,  spar,  and  killas       ...         12ft.       9in. 

5.  Gravel,  with  trees  and  branches  of  oak  of  great  size  at  the 

bottom        8ft.      Oin. 

6.  Tin  ground 8ft.       oin. 

7.  Clay,  in  which  were  found  the  roots  of  a  vast  oak,  and  a 

branch  4  feet  long  and  3  inches  in  diameter,  projecting 
from  the  wall  of  the  work.  A  second  mineral  deposit 
may  occur  below  this. 

E.  Mr.  Smith  also  gives  a  section  of  Pentowan  work  (either  a 
place  near  Pentuan,  or  a  misprint)  in  1807. 

Sandy  clay,  stones,  gravel        

Peat  with  roots  and  leaves       .. 

Sand  with  branches  and  trunks  of  trees         

Finer  sand,  with  shells,  bones,  horns,  vertebra  of  a  whale, 

human  sktills 

Coarse  gravel    

Close  sand  -n-ith  clay,  becoming  peaty  near  the  base     

Loose  etones  and  grave),  1  foot  thick,  resting  on  tin  ground. 


Oft. 

Oin. 

7ft. 

Oin, 

8ft. 

Oin. 

[2ft. 

Oin. 

2ft. 

Oin. 

.2ft. 

Oin. 

eft. 

Oin. 

8ft. 

Oin. 

6ft. 

Oin. 

12ft. 

Oin. 

31ft. 

Oin. 

eraging        4ft. 

Oin. 

...     7ft.  to  9ft. 

Oin. 

9ft. 

Oin. 

9ft. 

Oin. 

36ft. 

Oin. 

W.  A.  E.  Ussher — Pleistocene  QeoJogy  of  Cornwall.        47 

Falmouth  district. 

F.  Tregoney  Stream  Work  in  1807,  given  by  Mr.  Smith  [op.  cit.). 

1.  Granitic  gravel  with  layers  of  sand lift.     6in. 

2.  Black  mud  with  shells   (a  cow's  horn  and  horns  of  stags)       15ft.     Oin. 

3.  Tin  ground       averaging         2ft.     Oin. 

6.  In  Journ.  Eoy.  Inst.  Corn.  yoI.  iv.  p.  204,  etc.,  Mr.  Henwood 

gives  the  following  sections  in  two  places,  where  the  bed  of  Kestron- 
guet  Creek  is  some  12  feet  below  spring-tide  high-water. 
A.  Section  1. — 

1.  Mud  of  the  river,  very  soft 

2.  Mud  and  coarse  sand 

3.  Mud  (hardened) 

4.  Mud  (with  numerous  oyster  shells)    ... 

5.  Mud  (hardened) 

6.  Tin  p.  jund,  6  inches  to  6  feet  thick  ... 
Shelf  of  buii  or  blue  clay  slate. 

£.  Section  2.— 

1.  Soft  river  mud      

2.  River  sand  and  mud    

3.  Blue  mud  (shells  of  oyster,  cockle,  etc.) 

4.  Stiff  blue  mud  without  shells     

5.  Tin  ground ;  subangular  masses  of  granite,  slate,  elvan, 

quartz,  etc.,  and  tin  ore  in  large  masses  interspersed  with 
smaller  grains,  6  inches  to  6  feet  thick  ;     ...     averaging         4ft.     Oin. 
Shelf  of  clay-slate. 
De  la  Beche  (Report,  p.  403).    Up  the  Carnon  Valley  in  the  direc- 
tion of  St.  Day,  the  tin  ground  is  partly  covered  by  marine  sediments, 
partly  by  common  river  detritus. 

Carnon.  Mr.  Carne  mentioned  (T.R.G.S.  Corn.  vol.  iv.  p.  105) 
some  beds  of  slate  found  reposing  on  the  tin  ground  in  the  Carnon 
Valley,  unconnected  with  the  sides  and  bottom. 

C.  Mr.  Henwood  (T.K.G.S.  Corn.  vol.  iv.)  gives  the  following 
section  of  Carnon  Stream  Works,  the  letters  denote  beds  probably 
contemporaneous  with  those  in  the  Watergate,  Merry  Meeting,  and 
Broadwater  sections. 

a.  Sand  and  mud;    2  beds  ;    river  wash         

2.  Silt  and  shells ;    3  successive  beds      

3.  Sand  and  shells  (a  stream  of  fresh  water  percolates 

through  this  bed)      ...     

4.  Silt;    S'^beds        

5.  Sand  and  shells    

6.  Silt  with  numerous  shells 

7.  Silt  with  stones  in  places    

b.  Wood,    moss,    leaves,   nuts ;     dark    coloured    as    if 

charred;    a    few   oyster   shells;    animal    remains, 
chiefly  cervine ;    human   skulls.     Towards  the  sea 

this  bed  gives  place  to  silt  (No.  7) 1ft.       6in. 

e.  Tin  ground,  rounded  tin  ore,  unmixed,  and  in  a 
quartz  and  capel  (quartz  and  schorl)  matrix ;  from 
a  few  inches  to  12  feet  in  thickness  ;    ...   averaging  4ft.       Oin. 

Eounded  pieces  of  slate,  granite,  and  quartz,  mixed 
with  the  tin  stones. 
Mr.  Henwood  observes  that  above  Carnon  Section,  either  the  old 
forest  never  flourished,  or  it  has  been  destroyed  in  the  accumulation 
of  alluvia,  in  which  periods  of  peat  gi-owth  and  transport  of  vegetable 
matter  are  indicated. 

Mr.  E.  Smith  gives  a  section  of  Carnon  Works  in  1807  (Geol. 
Trans,  vol.  iv.  p.  404). 


3ft. 

Oin. 

Oft. 

lOin. 

2ft. 

Oin. 

12ft. 

Oin. 

3ft.  to    4ft. 

Oin. 

12ft. 

Oin. 

18ft.  to  22ft. 

Oin. 

48         W.  A.  E.  Ussher — Pleistocene  GeoJogij  of  Cornwall. 

7.  Sections  given  by  Mr.  Henwood  (J.  R.  Inst.  Corn.  vol.  iv.  pp. 
200,  201)  which,  from  similarity  of  names,  seem  to  refer  to  localities 
lying  between  Falmouth  and  Ilelston. 

A.  1.  The  Upper  part  of  Carn  Wartha, 

1.  Wom  and  unworn  granitic  detritus,  mixed  with  lumps  of 

peat,  and  refuse  of  previous  operations 12ft.     Oin. 

2.  Tin  ground— granitic  sand  and  gravel,  sprinkled  here  and 

there  with  waterworn  granules  of  tin  ore  ;  interspersed 
at  intervals  with  blocks  of  granite  and  schorl  rock       ...  12ft.     Oin. 

Shelf  of  disintegrated  granite. 

B.  At  Lezerea  in  Mean  Vroaz. 

1.  Peat;  vrith  nuts  and  branches  of  hazel  in  deeper  parts,  in 

places 4ft.     Oin. 

2.  Coarse  granitic  gravel  with  occasional  subangular  stones 

of  tin  ore 2ft.  to  3ft.     Oin. 

3.  Granitic  sand,  slightly  mixed  at  intervals  with  felspathic 

clay    ...  2ft.     Oin. 

4.  Tin  ground,  angular  and  subangular  masses  of  granite 

and  schorl  rock,  largely  mixed  with  tin  ore  of  different 

character  from  that  at  Cam  Wartha      3ft.     Oin. 

"  In  other  parts  of  the  Moor  sections  of  ancient  works  show  beds 
of  detrital  matter  resting  immediately  on  the  outcrop  of  tin-bearing 
veins  in  the  granite." 

C.  Near  Tregedna  in  Mawnan  (?  at  mouth  of  R.  Helford)  vegetable 
mould  and  hardened  silt,  20  or  30  feet  thick,  overlie  a  poor  deposit 
of  tin  ore  resting  on  slate  shelf. 

(Ihld.)  Waterworn  granules  of  pure  gold  have  been  found  in 
detrital  tin  ore  (which  is  less  rounded  than  in  other  parts  of  Corn- 
wall) near  Helston. 

Mr.  Henwood  (T.  E.  G.  S.  Corn.  vol.  v.  p.  129)  said  that  the 
valleys  between  Breague  Church  and  Porthleven,  and  from  Helston 
to  the  Loo  Pool,  have  been  streamed  for  tin. 

Penzance  District. 

8.  A.  Mr.  Henwood  {op.  cit.  p.  34)  gives  a  section  in  the  valley 
between  Huel  Darlington  and  Mai'azion  Mine  near  Newtown,  at  20 
to  30  feet  above  the  sea.  Sea  sand  with  shells  was  found  on 
vegetable  matter,  with  trunks  and  branches  of  oak,  willow,  hazel  in 
abundance,  resting  on  poor  tin  ground  on  shelf  at  about  the  level  of 
the  sea. 

B.  At  Tregilsoe  (Tregilliow),  on  the  confines  of  Ludgvan  and  St, 
Hilary,  a  section  of  the  short  shallow  vale  terminating  in  Marazion 
Marsh  is  given  by  Mr.  Henwood  (Journ.  R.  Inst.  Corn.  vol.  iv.  p. 
197).  Peat  about  6  feet  in  thickness  rests  on  the  tin  ground, 
divided  through  its  entire  width  by  a  thin  seam  of  clay,  impervious 
to  water,  and  running  obliquely  both  to  the  shelf  and  to  the  surface. 
Above  the  clay  seam,  the  gravel  consists  of  angular  and  subangular 
masses  of  slate,  quartz,  veinstones,  granules  of  cr^'stalline  tin  ore, 
all  imbedded  in  bluish  clay.  Below  the  clay  seam,  slate  pebbles 
still  prevail ;  elvan  nodules  are  not  uncommon,  but  the  quartz  is 
smaller  and  less  frequent.  Tin  ore  is  diffused  through  the  tough 
reddish-brown  clay  matrix.  Although  within  a  mile  of  granite  no 
trace  of  granitic  matter  was  found  in  these  works. 


W.  A.  E.  Ussher — Pleistocene  Geology  of  Cornwall.        49 

Land's  End  District. 

9  A.  (Hen wood,  op.  cit.  p,  195).  Near  Bejowans,  in  Sancreed, 
section  of  a  confluent  with  the  little  vale  from  Tregonebris  to  the 
coast  at  Lamorna. 

1.  Granitic  sand  and  gravel  with  small  angular  and  sub- 

angular  stones     6ft.  to  12ft.     Oin. 

2.  Peat  with  nuts,  branches,  and  roots  of  hazel      2ft.  to    8ft.     Oia. 

3.  A  few  inches  of  granitic  sand,  gravel,  and  pebbles,  with 

occasional  large  granite  boulders  like  the  tin  ground. 

4.  Tin  ground,  rounded  masses  of  felspathic  granite  and 

tin  ore,  fragments  of  veinstones  and  quartz  crystals     2ft.  to    9ft.     Oin. 

B.  Mr.  Henwood  (op.  cit.  p,  193)  mentions  the  sprinkling  of  tin 
ore  on  S.E.  of  St.  Just,  in  the  southern  and  central  parts  of  a  ravine 
trending  from  Kelynack  north-westward  to  Pornanvon.  He  gives 
a  section  at  Bosworlas,  in  a  narrow  strip  of  virgin  tin  ground. 

1.  Vegetable  mould,  in  some  parts  of  the  glen  succeeded  by  2ft.  or  3ft. 

2.  Granitic  gravel,  sprinkled  sometimes  with  tin  ore        ...  a  few  inches. 

3.  Tin  ground  of  granitic  matter,  subangular  and  rounded 

tin-bearing  veinstones,  pure  tin  stone,  subangular  or 

angular Sin.  to  2ft.     6in. 

The  surface  of  the  tin  ground  maintains  a  tolerably  uniform  sea- 
ward slope  throughout  the  ravine. 

C.  (op.  cit.  p.  196).  Between  Towednack  Church  and  Amellibrea, 
in  the  lower  part  of  Cold  Harbour  Moor. 

1.  Teat      2ft.  Gin. 

2.  Granite  detritus ;  mixed  with  blue  clay,  and  unproductive  in 

the  upper  part ;  buff  and  reddish  browTi,  with  a  little  tin  ore 

and  tin-bearing  veinstones  in  the  lower  part 3ft.  Oft. 

D.  On  Leswhidden  and  Bostrase  Moors,  Mr.  Came  (T.K.G.S. 
Corn.  vol.  iii.  p.  332)  mentioned  the  occurrence  of  alluvial  soil  6  to 
9  feet  in  thickness  on  the  shelf,  and  at  Numphra  Moor  not  exceed- 
ing 5  feet. 

10.  Mr.  Henwood  (J.  K.  Inst.  Corn.  vol.  iv.  p.  199)  gives  a 
section  of  the  bed  of  a  rivulet  at  St.  Erth,  near  Hayle,  as  follows,  the 
thickness  of  the  deposits  not  being  given :  Gravel,  sand,  and  mud, 
on  peat,  under  which  roots,  trunks,  and  branches  of  trees,  with 
quantities  of  mud,  were  found  resting  on  tin  ground,  poor  and  not 
extensive. 

Mr.  Carne  (T.  E.  G.  S.  Corn.  vol.  iv.  pp.  105-111)  gives  the 
following  general  notes  on  Diluvial  tin. — Cap  shelves  are  tabular 
masses  of  rock  projecting  from  sides  or  bottom  of  the  tin  ground,  so 
as  to  allow  of  the  occurrence  of  tin  ore  under  them. — Copper,  not 
found  in  tin  gravels,  probably  because  rarely  so  near  the  surface 
as  tin,  and  in  the  form  of  sulphuret  so  liable  to  decomposition. — The 
traces  of  gold  met  with  were  probably  derived  from  undiscovered 
veins  on  the  east. —  All  the  productive  streams  occupy  valleys 
opening  on  the  S.  coast,  whilst  most  of  the  richest  tin  veins  are 
near  the  N.  coast.  The  direction  of  the  tin  streams  seems  to  have 
been  from  N.N.W.  to  S.S.E. — In  narrow  valleys  little  tin  ore  is  ob- 
tainable. In  steep  valleys  all  the  ore  is  upon  the  shelf.  In  very 
gently  sloping  valleys  tin  ore  is  met  with  to  within  two  or  three 
feet  of  the  surface,  as  at  Cliyanhall.      In  gently  sloping  valleys  the 


50         W.  A,  E.  UsRhcr — Pleistocene  Geology  of  Cormcall 

tin  ground   is  thick  but  poor,  owing  to  admixture   with   alluvial 
sediments. 

General  Notes. 

As  the  stream  tin  gravels  were  deposited  during  the  last  stages  in 
the  elaboration  of  the  present  drainage  system,  their  watershed 
boundary  can  scarcely  have  differed  much  from  the  present ;  it  is, 
therefore,  only  natural  that,  whilst  the  richest  tin  veins  are  near  the 
north  coast,  the  most  productive  streams  occupy  valleys  opening  on 
the  south  coast. 

The  position  of  the  tin  ground  with  reference  to  the  sea-level  in 
the  estuarine  sections  is,  unfortunately,  seldom  given.  In  Mr.  Hen- 
wood's  section  on  Marazion  Green  {S  A),  mention  of  overljang  alluvia 
seems  to  have  been  omitted ;  as  Mr.  Carne,  in  a  section  at  Huel 
Darlington,  near  Mai'azion  River,  gives  twelve  feet  of  peat  and  gravel 
above  the  sea  sand,  and  the  surface  is  given  in  Mr.  Henwood's 
section  at  twenty  to  thirty  feet  above  the  sea-level,  the  top  of  the 
marine  bed  would  appear  to  be  a  few  feet  above  high  water  (Carne, 
T.  R.  G.  S.  Corn.  vol.  vi.  p.  230). 

Again,  in  Mr.  Smith's  section  (o  C)  of  Lower  Pentuan,  the  shelf  is 
said  to  be  at  low-water  level,  which  would  place  the  top  of  the 
upper  marine  bed  at  about  forty  feet  above  low  water,  which,  con- 
sidering the  absence  of  marine  deposits  at  Wheal  Virgin  Works  (5  B) 
and  Upper  Pentuan  (5  i>),  is  out  of  the  question  ;  so  that  either  the 
thicknesses  are  not  given  in  feet  and  inches,  or  the  level  of  the  shelf 
is  eiToneous. 

Mr.  Carne  (T.  R.  G.  S.  Cora.  vol.  iv.  p.  47)  describes  the  tin 
ground  of  Drift  Moor  Works,  near  Xewlyn,  as  resting  on  the  sides 
(which  come  to  within  a  few  feet  of  the  surface)  and  bottom  (forty 
feet  from  the  surface)  of  a  clay-lined  basin.  This  is  a  most  excep- 
tional phenomenon,  and  seems  to  show  the  great  erosive  power  of 
the  stream  tin  floods  rushing  into  and  deepening  a  depression,  very 
much  in  the  manner  in  which  giants'  kettles  are  produced  by  the 
pestle-like  friction  of  fragments  swirled  round  hollows  by  subglacial 
streams.  A  somewhat  analogous  phenomenon  is  mentioned  by  Dr. 
Boase,  which,  although  not  relating  to  stream  tin,  I  give  here 
(T.  R.  G.  S.  Corn.  vol.  iii.  p.  131) :  "A  person  surveying  the  Channel 
took  his  station  on  Wolf  Rock,  where  he  observed  a  cavity  resembling 
a  brewer's  copper,  and  containing  rubbish  at  the  bott(^i ;  it  was 
covered  by  the  sea  nine  hours  out  of  twelve." 

The  occurrence  of  an  oblique  clay  seam  in  the  tin  ground  at 
Tregilsoe  (8  B),  separating  accumulations  of  slightly  diflferent 
characters,  suggests  the  existence  of  bedding,  true  or  false.  The 
exceptional  occurrence  of  clay  shelf  (4  G  and  perhaps  5  D)  is  worthy 
of  note. 

The  changeable  character  of  the  deposits  in  stream  tin  sections 
precludes  the  absolute  correlation  of  individual  beds.  Inland  streams 
cannot  be  expected  to  furnish  such  sections  as  their  estuaries,  yet  it 
is  scarcely  safe  to  identify  tin  ground,  when  not  overlain  by  sedi- 
ments (as  9  C) ;  when  composed  of  fine  material  under  a  thin  cover- 
ing of  sediment  with  no  indication  of  a  land  surface  (as  in  4  G,  H, 


JF.  A.  E.  Ussher — Pkidoccne  Geology  of  Cornwall.        51 

1,  J,  and  9J5);  or  where  it  rests  on  outcropping  tin  veins  (as  7  B), 
with  the  stanniferous  gravels  of  Par  (o),  Pentuan  (5  A,  B,  G,  D), 
Caruon,  etc.  (6  A,  B,  G) ;  whilst  in  some  sections  stanniferous  deposits 
occur  at  different  horizons,  as  4  i?  (probably  5  B),  IB. 

To  synchronize  the  forest  remains  in  the  vai-ious  sections  is  unsafe, 
because  in  many  valleys  deposition  seems  to  have  gone  on  con- 
tinuously, or  to  have  been  interrupted  by  such  very  brief  periods  of 
peat  accumulation  or  undergrowth,  that  their  relics  became  entirely 
mixed  up  and  incorporated  with  the  succeeding  deposits,  as  in  4  B, 
G,  D,  E,  and  5  F;  also  4  J"  and  7  A. 

The  deposition  of  stream  tin  gravels  evidently  extended  over  a 
much  longer  period  than  is  represented  by  the  tin  ground ;  for  the 
very  irregular  wear  of  the  sides  and  bottoms  of  their  channels,  and 
the  existence  of  false  shelf  (4  D,  E)  here  and  there,  and  of  masses 
of  the  surrounding  rock,  the  apparent  debris  of  fallen  cap  or  false 
shelves  (4  A,  5  A,  G  G),  can  only  be  accounted  for  by  powerful 
streams  carrying  their  detritus  to  lower  levels,  and  occupying  the 
energies  of  their  upper  and  more  torrential  reaches  in  eroding  their 
banks  and  beds  into  such  irregular  shapes  as  the  unequal  durability 
of  the  rocks  permitted. 

In  like  manner,  the  duration  of  the  forest  growth  is  not  to  be 
measured  by  the  forest  beds  overlying  stream  tin  in  Marazion  Marsh, 
Pentuan  (5  A,  G),  etc.,  which  can  only  be  regarded  as  synchronous 
with  a  comparatively  short  part  of  the  period  ;  whilst  the  recurrence 
of  peat  beds  with  arboreal  remains  at  diflerent  horizons  in  the  stream 
tin  sections  (4  A,  B,  5  E,  7  B,  d  A,  10)  shows  that  even  after  the 
forests  fringing  the  coasts  were  submerged  and  buried  with  the 
peat,  which  had  accumulated  around  them  during  the  last  stages  of 
their  existence,  it  was  some  time  before  forestial  growth  in  inland 
districts  succumbed  to  unfavourable  climatal  conditions,  and  still 
longer  before  the  succeeding  undergrowth  gave  place  to  the  bare  and 
shrubless  chax'acter  presented  by  so  large  a  part  of  western  and 
central  Cornwall  now. 

Although  it  seems  only  reasonable  to  regard  the  deposition  of 
metallic  detritus,  as  now  going  on,  wherever  the  stream  channels  are 
traversed  by  tin  veins,  this  process  is  so  insignificant  that  as  a  whole 
the  stanniferous  gravels  must  be  referred  to  a  period  considerably 
posterior  to  the  raised  beach  formation,  and,  either  long  after  the 
culmination  of  the  elevation  during  which  Head  was  accumulated, 
or  in  part  synchronous  with  its  accumulation,  when,  through  greater 
elevation  and  increased  rainfall,  the  force  and  volume  of  the  streams 
was  greater.  The  commencement  of  the  forest  growth  is  also  in- 
definite, but  subsequent  to  the  accumulation  of  the  Head,  during  the 
prevalence  of  a  subsidence  which  produced  conditions  unfavourable 
to  the  existence  of  the  tin  floods  as  they  became  more  suitable  for 
its  extension.  So  that  the  forest  growth  may  have  begun  before  the 
stream  tin  floods  dwindled  away,  and  the  latter  may  have  been 
partly  contemporaneous  with  the  Head.  Whilst  marine  sediments  on 
the  forest  bed  or  tin  ground  in  estuarine  sections  (3,  5  A,  G,  E,  6  A, 
B,  G,  8  A)  prove  the  last  great  movement  to  have  been  one  of  sub- 


52         W.  A.  E.  Utisher — Pleistocene  Geoloyi/  of  Conucall. 

siclence,  the  more  orderly  arrangement  of  the  deposits ;  the  general 
absence  of  heavier  far-bome  detritus ;  the  entire  desertion  of  parts  of 
their  old  channels  by  some  of  the  present  streams,  indicate  the 
gradual  prevalence  of  conditions  more  akin  to  those  now  prevailing 
than  to  those  in  operation  during  the  deposition  of  the  stanniferous 
gravels. 

The  growth  of  trees,  some  ver^^  old,  on  the  surface  (5  C,  B),  shows 
that  the  latest  of  these  changes  must  have  been  some  time  in  opera- 
tion, whilst  the  presence  of  human  remains  at  great  depths  beneath 
the  surface,  at  Carnon  and  Pentuan,  and  the  tradition  respecting  St. 
Michael's  Mount,  would  seem  to  justify  the  belief  that  the  period  in 
which  the  forests  were  finally  submerged,  although  geologically  very 
recent,  is  yet  prehistoric. 

As  the  subsiding  movement  gradually  enabled  the  sea  to  circum- 
scribe the  forest  tracts  on  its  old  fore-shore,  the  beach  materials 
pushed  forward  would  finally  tend  to  bar  the  drainage  of  the  valleys 
opening  on  the  coast,  and  to  convert  the  low  lands  into  peat  mosses, 
forming  round  the  surviving  trees  till  the  further  advance  or  disper- 
sion of  the  beach  dams  permitted  the  sea  to  regain  its  old  coast-line, 
entombing  the  forest  fringes  and  their  peaty  surroundings  beneath 
its  sands.  Eliminate  from  this  all  changes  of  level  by  internal 
movements,  and  explain  the  entombment  of  the  forests  by  the 
lowering  of  level  consequent  on  removal  of  gravel  bars  releasing 
the  pent-up  drainage,  and  the  low  district  theory  is  presented. 
Without  changes  of  level,  however,  it  is  j)erfectly  untenable  as 
applied  to  Cornwall,  where  the  stream  tin  gravels  indicate  a  greater 
elevation  of  the  land  (5  B),  as  at  Carnon  and  Eestronguet  Creek  (6  A, 
B,  G),  for  instance,  where  the  tin  ground  is  more  than  sixty  feet 
below  the  sea-level,  whilst  the  estuarine  deposits  overlying  the  forest 
bed  prove  that  the  subsidence  was  progressive.  Also,  if  the  forests 
were  submerged  according  to  the  low  district  hypothesis,  they  must 
have  flourished  under  geographical  conditions  identical  with  the 
present,  and  yet  these  conditions  have  proved  unfavourable  to  their 
growth  on  the  present  low  lands. 

On  the  other  hand,  it  cannot  be  argued  that  the  submerged  forests 
are  mere  rafts  of  drift  wood,  stranded  with  vegetable  matter  borne 
down  by  rivers,  and  finally  buried  beneath  the  sea  sands.  The 
traces  of  submerged  forests  are  too  numerous  and  too  extensive  (1, 
7,  8)  to  be  thus  accounted  for ;  in  several  cases,  moreover,  the  roots 
are  said  to  occur  in  situ  (3,  5,  11,  ?  6),  and  the  elytra  of  beetles 
have  been  found  (1,  6).  Mr.  Godwin-Austen  (Q.  J.G.S.  vol.  vi. 
p.  93,  etc.)  says:  "It  is  diminished  area  and  elevation  which  at  pre- 
sent unfit  the  West  of  England  to  produce  that  growth  of  oak  and 

gigantic  fir  which seems  to  have  clothed  every  portion  of 

the  region  of  Dartmoor,  and  which  would  still  more  be  unfitted  for 
it  when  at  its  lower  Pleistocene  level.  On  such  low  districts,  how- 
ever, and  in  a  climate  modified  by  a  surrounding  sea,  some  portion 
of  a  previous  flora  might  have  been  enabled  to  live  on."  By  sub- 
stituting the  words  "  at  a  few  feet  below  its  present "  for  "  at  its 
lower  Pleistocene,"  the  passage  reads  in  accordance  with  my  ideas. 


63 


P»AR,T    V. 

Notes  on  Bloion  Sands  and  Gravel  Bars. 

Proceeding  round  the  coast  from  Plymoutli. 

1.  Par.  A  low  range  of  sand  dunes  separates  the  alluvial  tracts 
from  the  Par  sands. 

2,  Pentuan.  A  bank  of  coarse  granitic  sand,  with  bedding  and 
false  bedding  indicated  by  black  bands  of  schox'laceous  material, 
dams  off  the  sea  from  the  low  land  at  the  mouth  of  Pentuan  stream  ; 
on  the  landward  margin  of  the  low  tract  a  low  range  of  sand  dunes 
has  accumulated,  apparently  from  the  wind  drift  off  the  sand  bank  ; 
the  surface  of  the  alluvium  between  them  is  strewn  with  similar 
granitic  sand. 

3  a.  Falmouth.  At  the  curve  in  the  shore  at  Gyllyngvaes  (Clay- 
pole,  Proc.  Brist.  Nat.  Soc.  Ser.  2,  vol.  v.  p.  35)  the  top  of  the  gravel 
beach  or  bar  coincides  with  the  highest  spring-tides. 

h.  Swan  Pool  is  dammed  by  a  bar  of  small  quartz  pebbles,  80 
yards  broad,  and  in  the  highest  part  5  feet  above  high-water. 

c.  Mr.  Godwin-Austen  noticed  (Eep.  Brit.  Assoc,  for  1850,  Trans, 
of  Sects,  p.  71)  a  platform  of  bare  rock  near  Falmouth,  occupying 
an  intermediate  position  between  high-water  mark  and  the  base  of 
the  adjacent  raised  beach,  which  varies  from  3  to  10  feet  above  it. 

d.  Between  Pennance  Point  and  Maenporth,  rock  platforms  occur 
at  about  the  level  of  spring-tide  high-water,  the  traces  of  raised 
beach  in  the  vicinity  being  about  4  feet  higher. 

e.  South  of  Maenporth,  rock  reefs  and  platforms  were  noticed  at 
about  6  feet  above  oi-dinary  high-watei*,  the  base  of  the  adjacent 
raised  beach  being  10  to  15  feet  above  that  level. 

4.  A  strip  of  blown  sand  flanks  the  stream  at  Poljew ;  at  Gun- 
walloe  a  considei'able  accumulation  of  blown  sand  covers  high  land 
between  Castle  Mount  and  Towan.  On  N.W.  of  Castle  Mount, 
owing  to  the  exposed  situation,  no  blown  sand  occurs. 

5.  The  Loo  Pool  is  dammed  by  a  bar  of  small  quartz  pebble 
gravel  and  coarse  sand,  with  occasional  flint  and  slate  materials : 
coarse  brown  blown  sand  caps  the  low  cliffs  to  the  south  of  it. 

6  a.  Penzance. 

Dr.  Boase  (T.R.G.S.  Corn.  vol.  iii.  p.  131)  gives  a  section  of  the 
West  Green  sand  bank,  between  Penzance  and  Newlyn,  as  follows  : — 

1.  Granitic  sand,  of  quartz,  mica,  hornblende  slates  with  a  little  tin 

ore;   quartz  predominating 10  feet. 

2.  Gravel,  of  hornblende  slate  pebbles  from  1  to  3  inches  in  diameter, 

16  feet  thick,  resting  on  a  submerged  forest. 

He  points  out  the  difference  between  the  present  sea  sand  and 

that  forming  the  Green  sand  banks,  between  Marazion  and  Penzance 

and  Newlyn ;    the  former  being  finer,  and  composed  of  pulverized 

clay-slate  and   elvan,  whilst  the  latter  appears  to  have  been  derived 


54         W.  A.  E.  JJssher — Pleidoccne  Gcolofjij  of  Cornwall. 

from  the  destruction  of  a  continuous  band  of  granite  between 
Mousehole  and  Cudden  Point. 

The  original  length  of  the  Green  (op.  cit.  vol.  ii.  p.  136)  "was 
about  three  miles  on  the  east  and  one  mile  on  the  west  of  Penzance ; 
and  is  already  much  shortened.  The  ancient  breadth  is  unknown." 
The  West  Green  contained  but  two  or  three  acres,  and  in  no  place 
exceeded  130  feet  in  width,  when  Dr.  Boase  wrote  {op.  cit.  vol.  iii. 
p.  131,  etc.) ;  whilst  in  Charles  the  Second's  time  it  is  mentioned  in 
a  letter  to  Mrs.  Ley,  of  Penzance,  as  affording  36  acres  of  pasturage. 

h.  Mr.  Edmonds  (Edin.  New.  Phil.  Journ.  vol.  xlv.  p.  113,  for 
1848)  mentions  the  following  facts.  Seventy  years  ago  a  meadow 
lay  outside  the  present  sea-wall  at  the  entrance  to  Newlyn  ;  several 
houses  and  gardens  stood  on  the  seaward  side  of  the  cottages  at 
Sandy  Bank  in  Penzance ;  these  extremities  of  the  old  Western 
Green  are  no  longer  visible. 

In  181:3  a  sea-wall  was  built  by  the  Corporation  of  Penzance  to 
protect  the  remainder  of  the  sand  bank.  Off  the  eastern  bank 
numerous  rocks  between  high-  and  low-water  mark,  below  both  sand 
banks,  near  Newlyn,  Chyandower,  and  Marazion,  buried  beneath 
4  to  5  feet  of  sand  40  years  previous  to  1848,  were  uncovered. 

c.  In  the  sand  bank  between  Penzance  and  Marazion,  near 
Marazion  Bridge,  Mr.  Edmonds  discovered  a  great  number  of  land 
shells  {Helix  virgata  and  Bulimus  acutiis),  in  perfect  preservation, 
throughout  a  depth  of  about  10  feet  from  the  surface.  In  one 
instance,  in  the  same  locality,  he  observed  a  layer  of  small  rounded 
pebbles,  an  inch  or  two  in  thickness,  3  feet  below  the  surface  of 
the  sand,  and  more  than  15  feet  above  the  level  of  high-water.  In 
the  subjacent  sand,  for  4  or  5  feet  in  depth,  he  found  numerous 
perfect  land  shells. 

7  a.  Whitesand  Bay,  to  the  North  of  Sennen  Cove,  is  bounded  by 
sand  dunes,  capping  the  low  cliffs,  and  extending  for  a  little  distance 
inland,  surrounded  by  higher  ground. 

b.  On  the  north  side  of  Cape  Cornwall  rock  platforms  are  visible 
at  about  high-water  mark,  the  traces  of  raised  beach  adjacent  are 
about  6  feet  above  that  level. 

8.  Lelant,  Phillack,  and  Gwythian  Towans. 

"  The  Cornish  word  '  Towyn,'  says  Mr.  Edwards  (T.E.G.S.  Corn, 
vol.  vi.  pp.  300-304),  means  'a  turfy  down,'  the  word  'down'  being 
perhaps  a  mere  corruption  of  '  towyn '  by  the  very  common  change 
of  the  letter  t  into  d ;  and  it  is  remarkable  that  the  name  '  Les 
Landes,'  '  barren  heaths,'  given  to  the  sandy  districts  on  the  S.W. 
coast  of  France,  is  almost  precisely  the  same  with  '  Lelant,'  the 
2:»arish  in  the  Towans  where  an  ancient  market  town  is  said  to  have 
been  buried  by  the  sand.  Hence  Towans,  Downs,  Lelant,  and  Les 
Landes  may  all  be  regarded  as  synonymous." 

In  the  same  paper  he  characterizes  the  blown  sands  of  St.  Ives 
Bay  as  accumulations  of  comminuted  shell  sand  nourishing  a  scanty 
growth  of  Arundo  arenaria. 

a.  North  of  Hayle  and  west  of  Phillack  an  excavation  of  about 
30  feet,  at  the  termination  of  a  tramway,  afforded  me  a  good  section 


W.  A.  E.  Ussher — Pleistocene  Geology  of  Cornivall.        55 

of  the  blown  sanrls,  here  consisting  of  rather  fine  buff  sand,  made 
up  of  a  mixture  of  quartz  grains  with  comminuted  shells,  intersected 
by  numerous  dark  bands  near  the  top,  apparently  dipping  northward 
at  10'^,  as  though  caused  by  the  successive  entombment  of  rank 
grass  surfaces  under  gradually  accumulating  sand.  Below  the  dark 
bands  the  sand  still  presents  an  appearance  of  bedding,  such  as 
might  be  occasioned  by  successive  slips  from  an  eminence,  wherever 
the  slopes  became  too  sharp  for  the  accumulating  sand  to  rest. 
From  this  bedded  appearance,  and  from  the  frequent  linear  distribu- 
tion of  perfectly  preserved  land  shells,  (&.)  Mr.  Edmonds  [op.  cit.) 
considered  that  the  sand  in  its  gradual  accumulation  had  buried  the 
latter  "  without  ever  completely  covering  the  growing  turf  whereou 
the  animals  were  feeding  or  hybernating." 

c.  Mr.  Boase  (T.K.G.S.  Corn.  vol.  ii.  p.  142)  says,  "In  some 
l^laces  where  the  sand  has  been  bored  to  a  great  depth,  distinct 
strata  separated  by  a  vegetable  crust  are  visible ;  which  seem  to 
indicate  a  succession  of  inundations  at  distant  periods ;  but  it  is 
possible  ....  that  this  may  be  owing  to  a  local  shifting  of  the 
sands,  because  in  other  places  the  like  series  of  strata  is  not  found." 

d.  In  a  deep  cutting  in  the  sand,  about  a  mile  from  the  sea,  Mr. 
Edmonds  discovered  a  nest  of  small  land  shells,  50  feet  from  the 
surface,  of  the  following  species : — Helix  virgata,  Zonites  radiatulus, 
Bidimus  acutus,  H.  pulchella,  Zua  luhrica,  Vertigo  edentvla,  Pupa 
marginata,  P.  umhilicata,  P.  anglica,  Bitliinia  ventricosa. 

He  gives  the  following  list  (T.K.G.S.  Corn.  vol.  vii.  p.  71)  of  shells 
found  under  the  surface  of  Phillack  Towans  (those  marked  with  an 
asterisk  are  now  living  within  10  miles  of  Penzance). 


BuUmns  acutus. 

Eelix  fulva.* 

Vertigo  edentula. 

obscurus. 

fusca. 

palustris.* 

Carychium  minimum. 

hortensis. 

pygmma.* 

Clausilia  biplicata. 

Vitrina  pellucida. 

CoHOVulus  bidentattis. 

ptdchella. 

Zonites  alliarius. 

cellarius. 

Helix  aspersa. 

Pupa  anglica. 

•  nitidulus. 

caperata. 

pygmxus. 

rotundatus. 

Mr.  Edmonds  mentions  the  occurrences  of  numerous  shells  of 
Helix  pulchella.  at  depths  varying  from  1  to  30  feet,  in  various  parts 
of  the  sands,  and  says  that  living  specimens  have  been  observed, 
and  that  their  exuviae  have  been  found  in  Whitesand  Bay  sandhills 
as  well  as  those  near  Gunwalloe  and  Mullion,  Mounts  Bay,  and 
Gorran  (on  the  South  Coast  of  East  Cornwall). 

Mr.  Crouch,  who  identified  the  species  given  above,  observes  that 
Helix  pidchella  is  uncommon  in  the  locality,  that  it  has  been  found 
by  him  near  Fal  mouth,  at  Pendennis ;  and  near  Penzance,  at  Tre- 
reife ;  also  near  the  Land's  End. 

From  the  quantity  of  shells  found  in  so  small  a  space  in  the 
Towans,  Mr.  Crouch  considers  that  they  were  once  abundant  in  Com- 
wall,  but  are  now  gradually  becoming  extinct. 

Pupa  marginata  and  Bitliinia  ventricosa  he  alludes  to  as  rare,  a  few 
dead  sliells  having  been  obtained  by  him  at  Whitesand  Bay  (Land's 


56         W.  A.  E.  JJsslior — Pleistocene  Geology  of  Cormcnll. 

End)  and  near  Hayle,  but  that  no  live  specimens  have  been  found 
in  Cornwall. 

e.  Near  Godrevy  Island,  rock  platforms  are  visible  at  about  the 
level  of  spring-tide  high- water;  the  base  of  the  adjacent  raised  beach 
is  from  4  to  5  feet  above  ordinary  high-water. 

9.  Mr.  N.  Whitley  (25th  Ann.  Eep.  Eoy.  Inst.  Corn,  for  1843) 
mentions  "  the  succession  of  sand  hills,  principally  composed  of  com- 
minuted shells,  covering  about  1,500  acres,  on  the  north-east  of 
Perran  Forth.  The  inland  portion,"  he  says,  '•'  being  level  and  well 
sheltered,  might  easily  and  profitably  be  reclaimed  by  an  admixture 
of  clay  with  the  sandy  wastes,  as  in  Norfolk,  where  by  this  means  a 
free  sandy  loam,  forming  a  most  productive  soil,  has  been  oT)tained. 
Owing  to  the  extent  of  the  Perran  Sands,  being  more  heated  by  the 
sun's  rays  than  the  surrounding  districts,  in  calm  weather  by  the 
radiation  of  heat  from  the  sand  hills,  it  is  often  oppressively  warm 
at  the  Porth  during  the  early  part  of  the  night." 

10.  The  patch  of  blo-uii  sands  bordering  Hollywoll  Bay  may  be 
regarded  as  a  continuation  of  the  Perran  Sands,  it  is  partly  bounded 
by  a  stream. 

11.  The  flatfish  tract  between  New  Quay  and  Fistral  Bay  is 
covered  by  blown  sand. 

12.  Sand  dunes  occur  at  Porth  Barn,  Mawgan  Porth,  and  Porth- 
cothan,  Tregarnon,  and  Permizen  bays ;  they  are  very  insignificant. 

13.  Between  Constantine  and  Perleze  Bays  a  low  tract  is  covered 
by  blown  sand ;  as  exposed  near  Constantine  Island  (^vide  Eaised 
Beaches,  19  e),  it  is  4^  feet  in  thickness,  and  contains  layers  of  Patellae 
and  broken  Mijtili,  and  occasional  angular  slate  fi'agments  at  the  base. 

14.  The  low  tract  in  which  St.  Euodock's  Church  is  situated  is 
composed  of  blown  sand. 

15.  In  Perleze  Bay,  and  near  Port  Isaac,  rock  platforms  were 
noticed  at  about  ordinary  high-water  mark. 

General  Notes. 

"Wherever  the  area  covered  by  the  blown  sands  is  extensive,  we 
note  that  the  lands  generally  lie  low  with  reference  to  the  sea  or 
relatively  to  the  suiTounding  country  :  That  the  accumulation  spreads 
from  west  to  east,  and  only  occurs  in  considerable  quantity  in  locali- 
ties at  or  near  the  coast-line  facing  westwards. 

Thus,  in  bays  where  the  clifis  are  very  low  and  unbroken  by 
gorges  or  stream  channels,  facing  westwards  and  receiving  the  full 
force  of  winds  and  waves  of  the  Atlantic,  the  most  favourable  con- 
ditions occur  for  a?olian  transport  on  the  CoiTiish  coast. 

Naturally,  the  inland  extension  of  the  sand  depends  upon  the 
extent  of  low-lying  country  ;  but,  besides  this  check  on  its  extension 
exercised  by  barrier  hills,  running  water  and  the  growth  of  certain 
plants  may  arrest  its  progress ;  the  former  intercepts  the  fugitive 
grains  which  seldom  rise  more  tlian  a  few  inches  above  the  ground 
and  are  suspended  for  a  short  time  (De  la  Beche,  Picport,  etc.,  p. 
446).  As  to  the  latter,  Major  T.  Austin  (Proc.  Prist.  Nat.  Soc,  vol. 
ii.  No.  11,  for  Dec.  1867)  gives  the  following  plants  as  best  suited 


W.  A.  E.  Uss/ier — Pleidocene  Geology  of  Cornwall.        57 

to  arrest  the  inroads  of  blowing  sand,  in  some  cases  by  collecting 
hillocks  kept  together  by  their  matted  roots — Ammophila  arenaria 
(sea  reed) ;  Triticum  junceiim  (sea  wheat  grass)  ;  Hii^poplKB  rham- 
noides  (sand  thorn) ;  Cakile  maritima  (sea  rocket) ;  Salsola  kali  (salt; 
wort);  and  Sonclius  (sand  thistle). 

Mr.  Heuwood  (40th  Ann.  Eep.  Koy.  Inst.  Corn,  for  1858)  alludes 
to  the  progress  of  the  sand  drift  covering  the  low  lands  of  St.  Minver. 
on  the  east  of  Padstow,  being  checked  by  the  growth  of  Arundo 
arenaria. 

The  appearances  of  bedding  in  the  blown  sands  are  worthy  of 
note,  as  they  betray  the  incipient  characters  which  in  the  old  blown 
sands  of  Fistral  Bay  and  Gi'eenway  have  developed  on  consolidation 
into  marked  lamina?  or  thin  flaggy  sandstones,  and  near  Godrevy 
and  New  Quay  into  thick  beds.  Although  the  constant  shifting  and 
accumulation  of  the  sands  (8  b)  upon  a  growing  surface  must  be  true, 
yet  the  final  entombment  and  successive  growth  of  grass,  or  Arundo 
arenaria,  is  more  likely  to  have  been  occasioned  by  heavy  gales 
drifting  large  quantities  of  sand  upon  the  dunes  (8  c) ;  for,  constant 
shifting  of  particles  would  be  less  likely  to  produce  definite  layers  ; 
the  cohesion  of  the  particles  of  successive  surfaces  of  comminuted 
shell  sand  lending  itself  readily  to  the  formation  of  definite  beds,  and 
when  counter  wind  drifts  prevailed,  to  false  beds,  in  the  process  of 
consolidation  through  the  downward  passage  of  rain  v/aters.  But  as 
far  as  I  am  aware  no  traces  of  old  vegetable  surfaces  have  been 
found  in  the  old  consolidated  blown  sands.  The  false-bedded 
appearance  is  well  shown  in  the  old  blown  sands  of  Barnstaple  Bay. 
The  thin  layers  of  schorlaceous  and  quartzose  grains  in  the  sand 
bank  at  the  mouth  of  the  Pentuan  Valley  seem  to  be  due  to  marine 
action,  sorting  the  materials. 

The  absence  of  sand  or  gravel  bars  on  parts  of  the  Cornish  coast 
directly  exposed  to  the  waves  of  the  Atlantic,  and  their  limitation 
on  the  southern  coast  to  sites  where  promontories  and  headlands 
shelter  them  from  the  direct  influence  of  the  prevalent  winds,  and 
where  the  rapid  transport  of  shingle  is  lessened  by  projections  of  the 
coast  on  the  further  side,  is  worthy  of  note.  Thus,  the  West  Green 
bank  sheltered  by  the  Laud's  End  district  occurs  in  the  centre  of 
Mounts  Bay ;  the  Loo  Bar,  somewhat  similarly  sheltered,  has  been 
piled  up  where  the  southerly  trend  of  the  Lizard  coast-line  becomes 
pronounced ;  the  Swan  Pool  Bar  and  the  extensive  beaches  of  Fal- 
mouth, lying  between  the  flow  of  the  Fal  and  Helford  nearly  at 
right  angles,  are  sheltered  in  a  measure  by  the  Lizard  district,  and 
the  further  transport  of  shingle  is  checked  by  the  projection  of 
Pendennis  Point. 

The  set  of  the  coast-line  has  been  aided  by  the  inability  of  the. 
stream  waters  to  keep  a  seaward  passage  clear,  as  in  the  case  of  the 
Loo  Pool,  which  represents  the  ponded  drainage  of  the  Cober  and  its 
tributaries.  The  ceremony  of  cutting  the  Bar  annually  to  allow  the 
waters  to  escape  more  rapidly  than  by  filtration  through  it,  and  thus 
prevent  floods,  shows  how  efi'ectually  the  seawai'd  outlet  of  the 
stream  has  been  overcome.      The  finer  accretions  to  some  of  the 


58         W.  A.  E.  Uss/ter — Pleistocene  GeoIo(jij  of  Cornwall. 

banks,  as  iu  the  West  Green,  have  been  shifted  higher  by  winds  ;  a 
tongi;e  of  sand  occurs  on  the  east  of  the  Loo  Pool  similarly  drifted. 

The  surfaces  of  the  planed  Killas  reefs,  of  which  I  have  only 
given  a  few  examples,  occupy  in  most  cases  a  position  intermediate 
between  the  base  of  the  several  raised  beaches  in  their  vicinity  and 
high-water  mark  (3  c,  d,  e ;  7  6;  8e;  15).  Mr.  Godwin-Austen 
attributed  (Eep.  Brit.  Assoc,  for  1850,  Trans,  of  Sects,  p.  71)  their 
positions  to  a  recent  elevation  (preceded  by  a  subsidence)  of  not  more 
than  10  feet.  In  further  proof  of  this  he  cites  the  mud  beds  of  the 
Ese  and  Sussex  Ouse,  containing  estuarine  shells  at  slight  elevations 
above  the  present  sea-level.  The  occuiTenoe  of  many  of  the  rock 
platforms  are  explainable  without  invoking  changes  of  level.  The 
comparative!}'  recent  subsidence  by  which  the  forest  lands  were  sub- 
merged would  have  brought  again  within  the  influence  of  the  waves 
such  portions  of  the  old  platforms,  upon  which  the  raised  beach 
rested,  as  had  survived  the  intervening  subaerial  waste,  and,  whilst 
robbing  them  of  whatever  superimposed  deposits  might  have  existed, 
would  plane  anew  those  more  durable  portions  which  came  within 
the  influence  of  the  waves,  leaving  others  shorn  of  their  deposits, 
marking  by  the  heights  of  their  surfaces  the  seaward  slope  of  the 
old  plane  of  marine  denudation.  Bearing  in  mind  the  very  unequal 
heights  of  old  beaches  of  the  same  age,  and  the  irregular  levels  of 
their  platforms  in  places  at  the  base  of  the  same  cliff  (in  places, 
as  in  Fistral  Bay,  the  base  of  the  raised  beach  occupies  an  almost 
uniformlj' persistent  level),  except  where  great  discrepancies  in  their 
levels  with  reference  to  adjacent  raised  beaches  occurred,  the  plat- 
forms might  be  explained  as  above.  Other  phenomena,  however, 
whilst  in  no  way  interfering  with  the  above  explanation,  would 
appear  to  favour  the  idea  that  a  pause  in  the  downward  movement, 
after  the  submergence  of  the  forests,  was  succeeded  by  a  slight  con- 
trary movement.  Such  an  oscillation  might  serve  to  explain  the 
river  sediments  gaining  on  the  marine,  in  estuarine  stream  tin  sec- 
tions, and  to  enable  them  to  continue  pari  passu  with  a  resumption 
of  the  subsiding  movement.  If,  from  the  sections  in  Marazion  Marsh 
given  by  Messrs.  Henwood  (T.  E.  G.  S.  Corn.  vol.  v.  p.  34)  and  Carne 
{Ibid.  vol.  vi.  p.  230,  etc.),  we  may  place  the  top  of  the  marine  bed 
at  2  or  3  feet  above  high-water,  an  oscillation  Avould  alone  account 
for  its  position.  The  foiTuation  of  the  Warren  Sand  Bank  and 
Northam  Pebble  Ridge  might  also  be  explained  by  a  slight  elevation, 
whilst  the  rapid  diminution  of  both  would  seem  to  indicate  a  return 
to  the  previous  contrary  movement.  The  formation  and  diminution 
of  the  West  Green  Sand  Bank  might  be  similarly  explained. 

Mr.  Edmonds  (Edin.  New  Phil.  Joum.  for  1818),  commenting  on 
the  diminution  of  the  bank,  says,  that  300  years  ago,  in  Leland's 
time,  the  causewa}'^  leading  to  St.  Michael's  Mount  was  uncovered 
six  hours  out  of  twelve,  and  continued  so  for  220  years.  The  passage 
to  the  Mount  in  1848  was  open  four  hours  out  of  twelve,  and  often 
during  strong  S.W.  winds  covered  at  neap  tides  for  days  together. 
He  ascribed  these  rapid  changes  (6  h)  within  80  years  to  the  removal 
of  sand,  which  supported  the  western  side  of  the  ridge,  for  ballast 


W.  A.  E.  Ussher — Pleidocene  Geology  of  Cornwall.        59 

and  agricultural  purposes.  "  Some  idea,"  he  says  (T.  K.  G.  S.  Corn. 
vol.  vii.  p.  31),  "of  the  vast  quantity  of  sand  thus  abstracted  (for 
manure)  may  be  formed  by  the  fact  that  a  very  usual  clause  in  farm- 
ing leases  in  this  neighbourhood  is,  '  That  ten  butt  loads  of  sea  sand 
shall  be  spread  on  every  acre  whenever  it  is  broken  for  tillage.'  " 
This  explanation  is  a  very  plausible  one,  and,  coupled  with  the 
hypothesis  before  mentioned,  would  be  a  powerful  adjunct  in  ac- 
counting for  mox'e  rapid  recent  waste.  Great  quantities  of  commi- 
nuted shell  sand  are  also  carted  from  Bude  by  the  farmers  of  North- 
west Devon. 

In  conclusion,  I  have  to  express  my  sincere  thanks  to  Mr.  W. 
Whitaker,  Dr.  C  Le  Neve  Foster,  and  to  Mr.  E.  Parfitt,  of  Exeter, 
for  kindly  furnishing  me  with  all  the  information  in  their  power 
concerning  the  literature  of  the  subject;  to  Mr.  Robert  Hunt,  F.R.S., 
Keeper  of  the  Mining  Records,  for  placing  at  my  disposal  some  beauti- 
fully executed  sections  of  the  St.  Agnes  deposits  by  Mr.  A.  C.  Davies, 
some  of  which  I  have  submitted  to  the  Geological  Society  in  a  reduced 
form ;  also  to  Mr.  Horace  B.  Woodward  for  the  kind  interest  he  took 
in  this  paper  in  its  original  form,  and  the  information  he  obtained  for 
me  as  to  the  best  means  of  insuring  its  publication. 


Stephen  Austin  and  Sons,  Peinteks,  Hertford. 


O/v^^ 


C^tr^'^i  <*- 


2  Br,  J.  CroU—On  the  Cause  of  the  Glacial  Epoch. 

Greenland  from  the  sun,  if  none  were  cut  off  by  the  atmosphere, 
would  therefore  melt  50  feet  of  ice  per  annum,  or  50  times  the 
amount  of  snow  which  falls  on  that  continent.  What  then  cuts  off 
the  98  per  cent,  of  the  sun's  heat  ?  Is  it  clouds  and  fog  ?  If  so, 
why  do  not  these,  according  to  Mr.  Hill's  theory,  supply  sufficient 
beat  to  melt  the  small  quantity  of  snow  which  falls  on  Greenland  ? 
And  if  the  beat  is  not  cut  off,  and  far  more  than  sufficient  to  melt  the 
ice  reaches  the  ground,  why  is  not  the  ice  melted? 

Take  another  example.  South  Georgia  in  the  latitude  of  England 
is  covered  with  snow  and  ice  down  almost  to  the  sea-shore  during 
the  whole  summer,  and  yet  the  amount  of  beat  which  that  island 
receives  is  sufficient  to  melt  62  feet  of  ice.  Why  then  are  not  the 
snow  and  ice  melted  ?  Suppose  the  snowfall  there  were  ten  times 
greater  than  that  of  Greenland,  which  it  evidently  is  not,  yet  this 
would  not  amount  to  one-sixth  part  of  what  the  sun's  heat  could 
melt.  What  then  cuts  off  the  80  per  cent,  of  the  sun's  heat  ?  It 
cannot,  according  to  Mr.  Hill,  be  either  clouds  or  fogs,  and  if  the 
heat  is  not  cut  off,  the  question  returns,  why  are  not  the  snow  and 
ice  melted  ?  There  is  still  another  thing  to  be  explained.  The  snow 
falls  in  that  I'egion  in  the  very  middle  of  summer,  but  snow  would 
not  fall  unless  the  temperature  was  near  the  freezing-point.  Why 
then  have  we  such  a  low  midsummer  temperature,  notwithstanding 
the  fact  that  the  sun  is  in  perihelion  at  that  season  ? 

There  is  another  class  of  facts  utterly  at  variance  with  Mr.  Hill's 
fundamental  proposition.  The  lofty  peaks  of  the  Himalayas,  the 
Andes,  and  other  mountain  ranges  are  covered  with  perpetual  snow. 
There  coi:irn^i'Atively  few  of  the  sun's  rays  are  cut  off,  and  yet  the 
snow  is  peBfiftifel.  Few,  I  suppose,  would  admit  that  at  these  great 
eleva^ipn^e  than  50  per  cent,  of  the  sun's  beat  could  be  cut  off. 
But  i^WTper  cent,  reached  the  snow,  this  would  be  sufficient  to  melt 
50  feet  of  ice,  and  this  no  doubt  is  more  than  ten  times  the  quantity 
which  actually  requires  to  be  melted.  Why  then  does  not  the  beat 
melt  the  snow  ? 

I  have  little  doubt  that  if  Mr.  Hill  will  ponder  over  the  subject, 
so  as  to  find  out  a  satisfactory  answer  to  the  foregoing  queries,  be 
will  satisfy  himself  that  the  causes  to  which  I  attribute  the  Glacial 
Epoch  are  not  so  impotent  as  be  has  been  led  to  suppose. 


Stephen  Austin  and  Sons,  Printers,  Hertford, 


[^Extracted  from  the  Geological  Magazine,  Decade  IT.,  Vol.  YIT. 
No.  2,  p.  66,  February,  1880.] 


ME.   HILL   OX   THE   CAUSE    OF  THE   GLACIAL   EPOCH. 

By  James  Croll,  LL.D.,  F.R.S. 

IHxAVE  just  read  Mr.  Hill's  criticism  on  my  views  as  to  tlie  cause 
of  the  Glacial  Epoch,  and  have  to  thank  him  for  the  fair  and 
courteous  way  in  which  he  has  treated  the  subject.  I  fear  Mr.  Hill 
has  come  to  his-  conclusions  somewhat  too  hastily.  He  appears  to 
me  to  have  totally  misapprehended  the  real  eifect  of  fogs  and  a 
snow-covered  surface  on  climate,  and  also  the  influence  of  eccentri- 
city on  the  trade-winds.  But  I  must  defer  for  the  present  entering 
into  any  discussion  on  the  matter.  My  object  jnst  now  is  simply  to 
direct  attention  to  an  erroneous  assumption  which  appears  to  lie  at 
the  base  of  nearly  all  the  objections  which  have  been  urged  against 
the  theory  that  the  Glacial  Epoch  resulted  from  an  increase  of  ec- 
centricity. 

It  is  assumed  that  when  the  eccentricity  was  at  a  high  value,  and 
the  summer  in  perihelion,  more  snow  must  have  been  melted  than  at 
present.  It  is  assumed  that  the  quantity  of  snow  melted  must  be 
proportional  to  the  heat  received  from  the  sun.  Suppose  that  on  a 
certain  area  a  given  amount  of  snow  falls  annually.  The  amount  of 
heat  received  from  the  sun  per  annum  is  computed,  and  after  the 
usual  deduction  for  that  cut  off  by  the  atmosphere  has  been  made, 
if  it  be  found  that  the  quantity  remaining  is  far  more  than  sufficient 
to  melt  the  snow,  it  is  then  assumed  that  the  snow  must  be  melted, 
and  that  an  accumulation  of  snow  and  ice  year  by  year  in  this  area 
is  impossible.  To  one  approaching  this  perplexing  subject  for  the 
first  time  such  an  assumption  looks  very  plausible,  but  nevertheless 
it  is  one  totally  opposed  to  known  facts.  Take,  for  example,  Green- 
land. We  know  that  that  area  receives  from  the  sun  per  annum 
more  than  fifty  times  the  amount  of  heat  required  to  melt  all  the 
snow  and  ice  formed  on  it,  and  yet  that  countr}^  is  buried  under  ice. 
The  annual  precipitation  on  Greenland  in  the  form  of  snow  and  rain, 
according  to  Dr.  Kink,  amounts  to  onlj^  12  inches,  and  two  inches  of 
this  he  considers  is  never  melted,  but  is  carried  away  in  the  form  of 
icebergs.  The  quantity  of  heat  received  dt  the  equator  from  sun-rise 
to  sunset,  if  none  were  cut  off  bj'  the  atmosphere,  would  melt  3^ 
inches  of  ice,  or  100  feet  a  year.  The  quantity  received  between 
latitude  60"^  and  SO"',  which  is  that  of  Greenland,  is,  accordmg  to 
Meech,  one-half  that  received  at  the  equator.     The  heat  received  by 


n 


NIDDRY    LODGE  , 
KENSINGTON. LONDON.W. 

I 


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syof 


lore  rapid  deposition  of  strata  formed  from  their  waste— all  lue 
ssumed  as  certainties,  and  still  linger  in  some  parts  of  the  world 
ving  geologists  of  deservedly  high  reputation.     The  chief  object 


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inches  of  ice,  or  100  feet  a  year.  The  quantity  received  between 
latitude  fiO°  and  80°,  which  is  that  of  Greenland,  is,  according  to 
IMeech,  one-half  that  received  at  the  equator.     The  heat  received  by 


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lore  rapid  deposition  of  strata  formed  from  their  waste— all  these  were 
5sumed  as  certainties,  and  still  linger  in  some  parts  of  the  world  among 
vmg  geologists  of  deservedly  high  repntation.     The  chief  object  of  this 


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iceberg  ^  . 

to  sunset,  if  none  were  cut  off  by  the  atmosphere,  would  melt  3^ 
inches  of  ice,  or  100  feet  a  year.  The  quantity  received  between 
latitude  60°  and  80^,  which  is  that  of  Greenland,  is,  according  to 
Meech,  one-half  that  received  at  the  equator.     The  heat  received  by