When these shales have been much exposed to the weather and the rain has penetrated to some depth, or when after a fall of rain upon friable reef this is covered up by another slip, a very interesting chemical process is set up, viz.: the decomposition of the iron pyrites which is very plentifully distributed throughout the black shales. This decomposition sets up such an intense combustion that the shale _débris_ becomes red hot. This combustion I have known to last for months, even years, and the sulphurous acid gas evolved to be so plentiful that in damp weather or before and after sunrise it could be seen for many miles. To strangers looking into the mine this “burning reef” is a very startling sight, and many visitors of a superstitious turn of mind have often precipitately left in affright, on being jokingly told by miners when the latter were questioned about the heat, smoke and pungent sulphur smells—that the “Old Gentleman” was trying to break loose, or that they had come so near the “Old Gentleman” that he was now showing his anger. This and similar stories have often sufficed to scare away simple farmers from the place. On many parts of the reef the surface becomes heated to such an extent that articles placed upon it are almost at once destroyed. Laborers cannot work upon it at all without thick boots, and these even are destroyed in a few hours, while in many cases natives cannot by any inducement be persuaded to go near. The sudden combustion of coal in ships is caused by the very same agents, moisture and insufficient ventilation. These set up chemical change in the iron pyrites contained in the coal, and thus cause the explosions or fires at sea of which we frequently hear. This process of nature for reducing the iron pyrites is daily being imitated by the smelters in Spain and other countries, in the preliminary process for the reduction of the sulphur in copper ores, or copper pyrites. Some of the crystals of iron pyrites found in the reef shale are so very beautiful and perfect that they have been set in pins and other ornaments. After the black shale reef has been ignited by the above chemical means, and has cooled, it is as red as an ordinary clay flower-pot. It may be that the promoters of a brick company that was started here for the purpose of manufacturing bricks from the shales of the Kimberley mine, took their idea from the appearance of the shales when thus burnt by nature. The bricks made from reef, after being pounded and ground by heavy steam machinery, were latterly turned out of a very good quality, but the company collapsed, probably because they could not sell enough bricks to make it pay, as the high price of fuel rendered it necessary to charge £11, 10s. per 1,000, a nearly prohibitive price for ordinary building work.[25]