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