Brenton Symons’s 1863 map of the Liskeard mining district went under the grand title of
Geological map of the Caradon and Ludcott Mining Districts
But for those studying the subject of geology it appears to be sparse in geological information. Despite of it being published over 60 years after William Smith’s famous geological map of the Britain, no swaths of colour cross the map to denote the complexity of underlying strata, and no attempt is made to define the age of the rocks.
The reason for these omissions is focus. Brenton Symons’s geology only extended to the requirements of potential mine investors, and for their needs this map was perfect. And yet a close study of the map can reveal much about the geology of the area, and in some respects it contains more detail then the modern British Geological Survey maps.
In this post I will look at extracts from the map and explain what geological information can be extracted from this Victorian document.
The extract shows a small unsuccessful mine called Caradon Vale, that lay to the east of Caradon Hill, in Southeast Cornwall, UK. The UK Grid Reference is SX 29394 70992.
Prominent on the map is red lines denoting the course of the lodes. The dominance of these features is a reflection of the importance that the map’s purchasers would have placed in them. Lodes represented the potential for profits. Profits from either minerals or share speculation.
In Cornwall the east to west running lodes carried tin and copper, whilst north to south lead. So in this extract the mine was working three potential copper lodes, and one lead.
Arrows on the lode indicate the direction of underly; two of the copper underlay to the north, and one to the south. The longest lode is named ‘Caunter’, a name that indicates that it’s course is different from adjacent lodes.
The number 55 states the depth of the workings in fathoms, where one fathom is six feet. Other details of the mine relate to its operation rather then its geology. Pumping shafts, steam engines, the count house (Star) are shown.
Imposing into the western side of the map extract is an important geological detail, the granite/killas contact. This is denoted by the shaded line. To the west of this line is the granite intrusion of Bodmin Moor, whilst the rest of the map is in metamorphic rocks.
The BCG map Sheet 337 shows a more complex situation. Crossing the area in a northerly direction is a thrust fault with
Lower carboniferous of the Brendon formation to the west and upper Devonian of the Brook slate formation to the east. However, only two lodes are shown on the modern map, both carrying lead.
Simon’s map prospective buyers were not scientists interested in uncovering the geological past, instead this was a map whose buyers had a more limited interest in the ground beneath their feet. The map’s customers would have poured over its contents looking for where the next rich strike of copper, tin, lead or silver could occur. Today the detail it shows of the lodes around Caradon Hill forms a excellent supplement to the modern geological maps of the area.