The Geology of Caradon Hill- Cross-courses

This post continues the exploration of  the geology of Brenton Symons’ Victorian map of the Liskeard mining district’ with a wander around the cross-courses of the Caradon Hill area. My last post in the series came up with the conclusion that the modern British Geological map was more accurate than the 18th century publication, but a lot less pleasing on the eye. This post will put the two maps head to head on the topic of cross-courses.

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What is a cross course?
A cross course is a mineral vein running a near right angles to the predominant lode direction in an area. Cross-courses are normally non metallic but sometimes will carry lead and silver.

In Cornwall Cross-courses normally run in a north to south direction, apart from the in the St. Just area. Where a cross-course intersects a lode it throws it off its regular course; a break in the lode’s course called a ‘heave’.

Cross-courses gave mixed fortunes to a mine. Sometimes the heave would cause difficulties in tracing lodes,  they also could form a route for water to follow, a route that increased the risk of flooding workings.  On the plus side, cross-courses gave a line of softer rock for miners to follow, a weakness exploited to drive adits and cross-cuts.

Brenton Symons and Cross-Courses
Brenton Symons’ map denotes cross-courses by thick light grey lines. Their presence can also be detected by heaves in the lodes.  This post describes the location of the  cross-courses in the Caradon Hill area, and compares it with the information given in the contemporary Webb and Geach book,  and a modern BGS map. The cross-courses have been named by the mine setts through which they pass.

“There  are  several  cross-courses  running  through  the  country,  both  in  Killas  and  granite,  and  which  are found  as  is  usually  the  case,  to  influence  the  deposits  of  ore  wherever they  intersect  the  lodes.” Webb and Geach

The Cross-Courses

Wheal Pollard-Wheal Norris, Caradon Hill (Vale)

This long cross-course runs close to the main engine shafts of all three mines. Symons shows it becoming indistinct for a portion of its southern section, where he has assumed its course.

The British Geological Survey mao does not show the cross-course at all. The modern map does show some faults forming part of contact,

Webb and Geach mention the large cross-course in Wheal Norris and Caradon Hill mines. The latter mine used its weakness to drive an adit. Smaller cross-courses are mentioned in the book, but are not shown on the map.

Wheal Norris
This  sett  is  in  the  parish  of  St.  Cleer,  and  adjoins  Craddock  Moor  Mine,  having  the  same  lodes  traversing  it  for  500  fathoms  in  length.  There  are  in the  sett  nine  discovered  lodes,  which  are  at  right  angles  crossed  by  one  large cross-course  and  three  smaller  ones,  against  which  the  lodes  generally  make poor,  and  are  disarranged.

On  the  cross-course  directly  west  of  Carter’s  Shaft  a  cross-cut  has  been driven  north  40  fathoms,  intersecting  at  the  adit  level  two  large  masterly lodes

Caradon Hill
This  adit  has  been  driven  on  the  great  cross-course,  which  is  30  feet  wide, and  five  promising  lodes  have  been  cut,  producing  tin  and  copper;  it  is  still being  driven,  and  it  is  intended  to  proceed  with  it  through  the  entire  width  of the  sett,  with  a  view  to  cut  other  lodes  which  are  known  to  exist.

Craddock Moor-West Caradon
This cross-course cuts across the southeast corner of Craddock Moor’s sett, where Fox’s shaft is sunk on its course. No heave is evident on the lodes.

Yet again the BGS do not denote the existence of the cross-course. And yet again Webb and Geach describe more cross-courses than those shown by Symons.

Craddock Moor
There are  five  cross-courses  known  to  intersect  the  lodes,  three  of  which  are  from Caradon  Consols  which  is  immediately  south.

Gonomena-West Caradon

A consistent heave is shown by Brenton Symons; all the lodes western portions are displaced northwards. The BGS do not show the feature. Brenton Symons names it has the ‘West Caradon cross-course’ and the ‘Great Cross-course’ , ad states the feature was used to work the mine, and that it gave a heave if 2 to 6 fathoms. As in the previous cross-courses it is apparent that the  Victorian map only displayed the most significant cross courses.

Gonomena
The  boundary  cross-course  is  in  the  eastern  ground,  and  has  a  left-hand heave  displacing  the  lode  about  seven  fathoms.  West  Caradon  cross-course runs  through  the  centre  of  the  sett,  causing  a  right  hand-heave  of  about  three fathoms.  In  the  western  ground  three  other  cross-veins  come  in  from  West  Caradon and Craddock Moor, but these have not yet been seen in the mine.

West Caradon
These  lodes  are intersected  at  right  angles  by  numerous  cross-courses,  one  or  two  being  of a  large  size,  heaving  the  lodes  to  the  right  from  2  to  6  fathoms.  The  great cross-course  which  runs  through  the  centre  of  the  mine,  has  been  of  the  up most  service  in  working  the  mine  both  quickly  and  economically,  the  crosscuts  driven  on  its  course  costing  from  about  50s.  to  60s.  per  fathom,  which would  otherwise  have  to  be  driven  through  the  hard  granite,  at  a  cost  of  £12 or £14 per fathom.

South Caradon

This is Y shaped cross-course runs up the eastern slope of the Seaton valley, passing close to Jope’s shaft, and through Sump Shaft. The split of the Y is close north of Sump Shaft. The Cross-course causes the lodes western portions to be heaved norhwards.

This is the only cross course shown by the British Gelogicalk Survey. BGS show a single Cross-course running on the east of the Seaton River. It enters Gonomena set where its is heaved by a lode and then follows the western side of the openworks for a short distance. This coincides with the South Caradon Y cross course and a part of the great cross course. The gap in between the cross-courses shown by Symons coincides roughly with the heave shown by BGS

South Caradon
It will be seen that the whole of the Caradon lodes traverse  the  sett,  bearing  about  8°  north  of  west.  These  are  intersected  at  right angles  by  several  cross-courses,  the  easternmost,  near  Jope’s  Shaft,  heaving all  the  lodes  to  the  right  hand  regularly

The Great Cross-course

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South Caradon-Gonomena-South Phoenix-Phoenix
This cross course extends across a large portion of the map, from South Caradon to Phoenix. Its southern section, where it is called the boundary cross-course, is not directly shown by Brenton Symons. It can be identified however, by a heave in the lodes beneath the Seaton River.

This cross-course is shown only by the BGS in its southern section as it passes through the South Caradon and Gonamena Setts.

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South Caradon
Greenhill  Lode  is  driven  west  at  the  125  to  the cross-course about fathoms in length, 85  and contains  green  carbonate, grey  ore,  and  rich  oxide  of copper;  the  154  and  166 are  being  driven  to  get  under  this  ore,  in  the  confident  expectation  of  making  large  returns.  One  of  the  great  objects  of  the  adventurers  is  the  driving  of  the  126  cross-cut  south  on  the  great  cross-course, to  cut  Rosedown  and  Marke  Valley  lodes.

Phoenix
in a  deep  valley  streamed  for  tin,  is  a  large  cross-course  –  a  continuation,  in  fact, of  the  West  Caradon  boundary  cross-course,  which  there,  as  well  as  in  South Phoenix,  heaves  the  lodes  to  the  left  hand  about  10  fathoms.  This  crosscourse  is  many  fathoms  wide,  but  has  never  been  seen  at  the  Phoenix  Mines; as,  although  they  have  driven  on  a  course  of  ore  close  to  it,  they  were  afraid to  proceed,  on  account  of  the  probable  great  influx  of  water  that  would  ensue.

Wheal Hooper-South Caradon

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This cross-course may hold a clue to a mystery engine house. Its northern termination is close to the location of an isolated chimney whose purpose is not known. Symons shows and engine house located on the cross-course, a location that suggests that a shaft may have been sunk there in order to serve a cross-cut driven on the cross-course. This possible explanation for the mystery chimney is supported by the fact that the cross-course proved to be of great use to Wheal Hooper.

This is another cross-course is not shown by BGS.

Wheal Hooper
A cross-course,  which  has  been  of  considerable  utility  in  working  the  mine inexpensively,  stretches  across  the  sett,  bearing  a  few  degrees  west  of  north, and  intersecting  the  lodes  obliquely.  It  is  of  inconsiderable  magnitude,  and does  not  appear  to  affect  the  lodes  to  any  great  extent. WG

Glasgow Caradon

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Brenton Symons shows three cross courses, each one associated with shafts or adits.  The eastern cross-course has a heave of the western parts of the lodes to the north. This heave is similar to that shown on other cross-courses, that is the ground on the western side in moved northwards, or the eastern southwards.

Non of the Glasgow Caradon lodes are shown by BGS.

“He  drove  an  adit  south  on  a  large  crosscourse  about  four  feet  in  width,  and  cut  several  lodes.”

“A  cross-cut  from  the adit  has  been  driven  north  on  a  cross-course,  in  which  two  lodes  with  a  north underlie  have  been  cut,  containing  kindly  looking  gossan.

Marke Valley Consols
The Victorian map appears to show a short cross-course running northwards from one of the lode, close west of the dressing floors. Webb and Geach describes a cross-course that crosses all the lodes, a description that does not coincide with the map details.
No cross-courses are shown by BGS.

“South of  these  are  three  known  lodes,  one  of  which,  named  New  Lode,  has  been worked  to  the  80;  the  other  two  have  been  nearly  intersected  by  the  crosscourse  which  crosses  the  lodes  at  right  angles,  and  is  a  little  west  of  the  old whim shaft.”

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1 Wheal Pollard-Wheal Norris, Caradon Hill (Vale)
2 Craddock Moor-West Caradon
3 Gonomena-West Caradon
4 The Great Cross-course
5 South Caradon
6 Wheal Hooper-South Caradon
7 Glasgow Caradon
8 Marke Valley Console

Brenton Symons shows more cross-courses then the BGS, but less then those listed by webb and Geach.
Where a cross-course causes a heave, the ground to the west is northwards.
The cross-courses have been utilised by many of the mines for driving cross-cuts or adits.

Brenton Symons V British Geological Survey

Brenton Symons has the upper hand for this one. The Victorian map shows six cross-courses, whilst the BGS only one. The details described within the pages of Webb and Geach give credibility to the cross-course positions shown by Symons.  Therefore when it comes to cross-courses the Brenton Symons map is far superior to its modern counterpart.

Brenton Symons 1- BGS 1, Now a draw. Next round will be the elvans. 

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