Page:Transactions of the Geological Society, 1st series, vol. 3.djvu/138

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chalk, as seen in the Isle of Wight and Isle of Purbeck, which are distinguished from the higher beds of the same formation by their very superior consolidation. It is impossible for any two portions of the same formation to be more entirely identified, by every external character and by the fossils and organic remains contained in them, than are these Irish beds, which have been frequently called white limestone, with the English chalk in the above places: there as in England the lowest beds are destitute of flints which the upper contain in abundance.

2. Mulattoe, an arenaceous stone, with a calcareous cement, of a speckled appearance (whence its name) derived from numerous disseminated spots of green earth. It agrees altogether in its character and fossils with the green sandstone, which occurs in a similar geological position underlying the chalk in England: the thickness of this deposit appears to vary very considerably, and has not in any instance been precisely ascertained.

The numerous beds of coarse calcareous oolites, which in England succeed this green sandstone, are entirely wanting in Ireland, and the mulattoe reposes immediately on the lias limestone. Analogous circumstances are not however wanting in England. In the neighbourhood of Lyme Regis, in Dorsetshire, the sandstone has extended itself over the cut goings of the oolites, rests upon the lias in a manner similar to that just described; and as it is covered with beds of chalk, the whole section affords an exact counterpart to that presented by the Irish series.

3. Lias Limestone, a blue argillaceous limestone disposed in thin beds, alternating with slate clay, and distinguished by the ammonites, gryphites and the remains of the pentacrinus, which it abundantly contains. It may be worthy of remark that the sections given by Guetard and Monnet in the Atlas Mineralogique de la France, and the accompanying description, clearly prove the