MEGALICHTHYAN PERIOD. 175 



But in the Yoredale rocks which come on above, the drift 

 which is still most prevalent in the north, there yielding thick 

 sandstones, shales, coal and ironstone between the limestones, 

 is abundant in Ingleborough and farther south. It is however 

 more argillaceous, less arenaceous, and yields much less trace of 

 coal, circumstances which agree with the view that the land was 

 to the north, the deeper ocean to the south. The plants which 

 accompany the coal are for the most part of terrestrial growth. 

 None of them are known to stand erect in place and attitude of 

 growth, so as positively to mark the fact of the elevation of land 

 in any part of the Yorkshire district of mountain limestone. 



The life of the Period was still for the most part marine, and 

 consisted, beside a few fucoids, of many Zoophyta, Crinoidea, and 

 Mollusca, a few Annulosa and Trilobites, with a small number of 

 rather large cartilaginous fishes. A few land plants are found 

 in some of the alternating shales and sandstones, but not in their 

 place of growth. 



Marks of the existence of neighbouring land grow stronger con- 

 tinually as we ascend through the next mass of Palaeozoic strata 

 the millstone grit which contains more abundant remains of 

 plants and greater variety of sediments, such as rivers might 

 transport, especially quartz gravel beds in great thickness, for 

 such is really the basis of our millstone grit. In the next class 

 of deposits, or the Coal formation, we have proof of land in 

 Yorkshire, for among these deposits are certain strata of sand- 

 stone in which the stems of trees stand erect, and beneath several 

 of the coal-seams are the roots of trees extended in their natural 

 positions. The coal beds are certainly composed of terrestrial 

 plants, probably accumulated round the trees and above their 

 roots, often by the agency of water, which has left parts of its 

 living tenants even in the substance of the coal, as the defen- 

 sive fin-bones of cartilaginous fishes (Gyracanthus) and estuary 

 shells (Unionidse). But there is no reason from these facts to 

 infer that the land was greatly elevated. A low and even swampy 

 region only just raised above the flow of waters may be admitted 



