During the late stages of the cooling of the mass of granite that makes up a lot of Cornwall, fissures opened up in the granite when it was still molten, and more hot molten rocks bubbled up through the granite from the earth's interior. These new rocks contained many minerals, and as they crystallized they formed mineral lodes - tin, copper, zinc, lead and iron with some silver. Because the ore bearing rocks formed in this way, rather than being sedimentary rocks like coal (hence coal is laid down in great flat plates), they have to be mined vertically rather than horizontally. Each fissure has to be mined straight down into the earth and therefore needed a separate mine. Therefore a great many vertical shafts were needed, rather than the one shaft that tended to be used in coal mining.
Bronze is an alloy containing copper and tin, and mining of these metallic elements took place from the days of the “bronze age”. Mining in Cornwall dates back to between 1000 and 2000 BC when Cornwall is thought to have been visited by metal traders from the eastern Mediterranean, who named Britain, the 'Cassiterides' - 'Tin Islands' (Earl 1968 p.9). Cornwall and the far west of Devon provided the majority of the United Kingdom's tin, copper and arsenic. Originally the tin was found as alluvial deposits in the gravels of stream beds, but eventually underground working took place. Tin lodes outcropped on the cliffs and underground mines sprung up as early as the 16th century.
Eventually, the mine shafts dropped below the level of the water table, and the water had to be pumped out if mining was to continue any deeper. Hence pumps, and the houses for the engines that drove the pumps, were a necessary part of mining. These engine houses were the sturdiest buildings in the mines, as they had both to house the machinery and support the massive beams that worked the pumps. It is not surprising that so many engine houses survive in Cornwall. Some of these so-called 'Cornish pumping engines' were used in NZ, including in Thames. [There is a DVD outlining the history and technology of these pumps in The Treasury collection, and remnants and history of 'the big pump' can be seen at the Bella St Museum in Thames.]
As in Thames and other early NZ mining areas, conditions were harsh and the work was very hard. Given that most of the mines were narrow and vertical, many did not have cages to haul the miners up and down; instead access to the mine was by ladder, a tiring part of the daily toil of the miners:
'The simple ladders, which were the only means of descent and ascent from depths of up to 250 fathoms (1500 feet) in all Menheniot's [near Liskeard] mines, presented a very real accident hazard. … Generally accepted rates of ascent were 100 fathoms in 20 to 30 minutes, which at Wheal Mary Ann's [name of mine] ultimate depth would have involved a difficult and tiring climb of 50 to 75 minutes for each miner.' (Bartlett 1994 p.85)
Whole families were often employed in mining:
'A great mine dominated the lives of hundreds of men, women and children who lived in the neighbourhood of it. Whole families looked to it for their sole support. … At an early age, eight years and upwards, children of both sexes were apprenticed to it, doing light jobs about the surface. … At twelve or fourteen years of age, the boys proceeded [to become] underground miners, going below with their fathers … The girls, too, as they grew older, continued to work on the surface as “bal* maidens”, doing the heavy work of “spalling”, or breaking the copper ores, an occupation at which they normally remained until they were married.' (Hamilton-Jenkin 1927 p.131)
* 'Bal' is a Cornish term for a mine.
The Cornish Pasty was used originally by the miners as their food underground. It was easy to carry, and could have savoury in one end and sweet in the other.
At the various mining museum attractions in Thames, there seems to be a tendency to describe mine tunnels etc dug by miners of Cornish extraction, as being very small; implying that the miners themselves were very small. The following quotations pertain to this issue:
'The streamer [miner of alluvial ore in streams], like the modern china clay worker, was generally a man of fine build and splendid health, engendered by open-air work and the action of piggal (beat axe) and visgey (pick) in expanding his muscles. It was the streamer, rather than the miner (who, although wiry, is generally slight) who won for Cornishmen that reputation for wide shoulders which is said to have made a Cornish regiment take more room on the parade ground than any other.' (Hamilton-Jenkin 1927 p.64)
'The regulation size of a drift or level in 1670 was seven feet high and "three foot over" [wide, presumably], allowing room for two shovelmen and three bealmen to work at a time. Many of the workings, however, especially the adits, were "scarce half as large" and as in the "Conquer" set of branches at Wheal Fortune the ancient levels were "so extremely narrow that it would seem scarcely possible for a man to go through them". Further instance of the same sort may be seen today in the "old men's" crosscuts at Great Work mine, which in many places are not more than four feet high and two feet four inches across in the widest part. They were, as it seems, purposefully driven egg-shaped so to allow room for the hands in rolling barrows ...' (Hamilton-Jenkin 1927 p.87)
It would appear from the above that, although Cornish underground miners may have been slightly smaller than their above-ground counterparts, they would not have been appreciably smaller than was the norm for Englishmen of those times. A more likely explanation for the supposed minimalist approach to digging is probably related more to saving time and economy of effort. This was presumably because a large proportion of them were 'tributers' who were paid on the basis of the amount of ore they extracted.
Copper mining in Cornwall reached its peak around 1850, before foreign competition depressed the price of copper, and later tin, to a level that made Cornish ore unprofitable (Earl 1968 p.10, Barton 1968 p.7). At its peak, the Cornish mining industry had around 600 steam engines working to pump out the mines. Over 4000 men, women and children were employed just in the mines around Carradon Hill, on the Bodmin Moor. The demise of copper mining in the 1860s resulted in whole families leaving the area - often emigrating to other parts of the world. This period coincided with the opening of the Thames goldfield in 1867, and was the reason why many Cornish miners made their way to Thames; some directly, and others via other mining ventures, such as South Africa, California and Australia (Hamilton-Jenkin 1927 pp. 321-340).