OF THE COUNTIES OF NORTHUMBERLAND AND DURHAM. 223 
tained in the equivalent bed in Germany, has, without doubt, 
given rise to this supposition ; but if this had been the case, 
would not the bony covering have been considerably eroded, if 
not entirely destroyed ? and might not considerable quantities of 
metallic sulphurets be expected to occur in this bed in connec- 
tion with the fishes? In the marl-slate of this district, however, 
such metals are rarely found, and no signs of erosion are observa- 
ble on the scales. In whatsoever way they were destroyed, it is 
most probable that they floated in the water till the internal parts 
were destroyed, and that they were driven towards the sea by 
sudden floods along with the sediment in which they were finally 
embedded. The preservation of a Lingula and a few fucoid 
plants, the stems of some of which are nearly upright, clearly 
prove that this bed was deposited along some coast and its simil- 
arity in appearance and mineral composition to some of the coal- 
measure shales probably indicates the sources from which it was 
derived. 
In a few localities, as at Clack’s Heugh on the Wear, the Marl- 
slate is entirely absent, and the lowest bed of limestone, which is 
seen in one part of the section resting on the sandstone, is very 
thin and earthy. In most localities, however, this lowest bed of 
limestone is very hard, compact, pure, of great thickness, and 
strong-bedded. On this account it is extensively quarried 
in many parts of the escarpment, where it is generally well ex- 
posed, as it is also in the well-known outlier near Whitley, in 
Northumberland. It contains a few fossils identical with species 
which are found in some of the higher beds of the formation. 
This bed has been identified with the German “ Zechstein,” to 
which it is related both in position and fossil contents ; and it is 
succeeded by a large series of beds of limestone and yellow marl, 
which it is not possible to separate from it either by a natural 
line of demarcation, or fossil remains; it might therefore, 
perhaps, be more correctly grouped with the following extensive 
_ Series of beds of limestone and yellow marls which are well 
known by the distinctive term “ Magnesian-limestone,” as many 
of them contain a considerable portion of carbonate of magnesia 
