VEGETABLES. 181 



In some of our ironstone seams, particularly in the clifF at 

 Saltwick, vegetable impressions are very common. The plants are 

 often larger than those in the coal shale ; though in both there is 

 a mixture of plants of various sizes and kinds. The irajiressions in 

 the ironstone are usually better defined, and, from the hardness of 

 the stone, are more easily preserved than the specimens in the shale. 

 The substance of the plant is here also generally blackish and 

 bituminous, though impregnated with iron. The stems, leaf-stalks, 

 middle ribs of the leaves, and other thicker parts of the plants, have 

 undergone, in most specimens, a double transformation; having been 

 converted into a sparry substance, partly black and partly whitish, 

 which has been subsequently dissolved, and is now found in the 

 form of a fine powder, retaining the same colours. The mixture of 

 the black and white parts presents a curious appearance, the black 

 exhibiting numerous cracks, both longitudinal and transvei'se, as in 

 charred wood, while the white fills up these cracks. In several 

 instances, the spar has not been decomposed, but remains in its 

 original crystalline state. 



Similar petrifactions occur in the sandstone, but in less quantity. 

 The best vegetable impressions are in the harder beds of sandstone, 

 particularly some of the crow-stone beds ; but, as may be expected, 

 we seldom meet with such delicate and well defined impressions in 

 the sandstone, as we see in the ironstone or the shale. 



If we suppose, with some authors, that the beautifully ramified 

 substances in our moss agates, have been real vegetables, which, by 

 some unknown natural process, have been enveloped by a solution 

 of flint, and preserved in their form and colour while it has crystallized 

 around them, — we shall find here another class of vegetable remains, 

 much more delicate than those now mentioned. Great numbers of 

 these moss agates, or jasper agates, as they are also called, are 

 washed out of the alluvial cliflfe, in nodules of various sizes, generally 



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