Letter | Published:

Pipe-Clay

Abstract

I WAS forcibly struck the other day by the analogy between the beds of plastic clay (called here pipe-clay) which are every-where met with interstratified with the different drifts of wash-dirt, river-sand, &c., in the tin-mines about this country, and what was then to be seen in our own mine here. The mine had been under water for about a month. On pumping the water out, we discovered a layer of particularly fine, soft mud, four inches in depth, of about the consistency of cream. It is evident that any animal or vegetable substance dropping into this layer would sink through it and rest on the bottom. The pipe-clay contains no fossils except portions of trees which rest on the bed beneath it. Now, from the evidence before me here, I am led to the conclusion that the beds of pipe-clay were formed under like circumstances as these. The old torrents which brought the drift down from the mountains were undoubtedly continually changing their paths as they traversed the valleys, being dammed by accumulations of timber and boulders, thus causing the diversified and mixed-up appearance of the beds, some of them containing huge trees and heavy stones: these are the beds which contain the richest deposits of tin ores, others being beds of fine quartz sand, with beds of materials graduated between the two descriptions, and the beds of pipeclay interspersed. These last vary considerably in depth. I have seen them all thicknesses between one inch and twenty feet.

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