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COAL. 303 containing bitumen, carbonaceous matter, and vege table fragments. In the clays, imbedded nodules, or distinct strata of argillaceous ironstone often occur, and in conspicuous quantities ; forming the principal supply of ore for the iron-foundries. Galena and blende are sometimes found with the ironstone, as is pyrites in the coal itself, as well as in the accompa nying strata ; being the not infrequent cause of spon taneous combustion. When porcelain jasper exists, it must be considered as a casual and artilicial mineral, produced by this cause. The most singular, as the rarest mineral, observed in this series, is that inflam mable substance called Hatcheline, imbedded in very small quantities in the ironstones. Though the coal series is situated between the older and newer red sandstones, it is impossible to give an universal description of its geological connexions. The exact relations, distribution, and number of the strata, throughout even Europe, are far from being satisfac torily ascertained; and as to the world at large, our ignorance is still greater. The difficulty has been much increased hy r confounding the upper deposits of coal, here ranked as lignites, with those of the present series ; the mineral alone, as is too common with ge ologists, having formed the chief object of atten tion, to the exclusion of the geological characters and positions. I must therefore limit this description to Britain, where the subject has alone been accurately studied ; and thus, supposing the series complete, the old red sandstone and the mountain limestone are fol lowed by the coal series, to which succeeds the mag nesian limestone and the red marl, and, subsequently, such other strata as may be present in that particular tract. Now it is essential to remark, that the old red sand-