390 
ELEMENTS OF GEOLOGY. 
ichth 3 ^olites, which are very entire and well preserved, will 
be found. Even a single scale is usually so characteristically 
marked as to indicate the genus, and sometimes even the par¬ 
ticular species. They are often scattered through the beds 
singly, and may be useful to a geologist* in determining the 
age of the rock. 
SCALES OF FISH. MAGNESIAN LIMESTONE. 
Fig. 420. Fig. 421. Fig. 422. Fig. 423. 
Fig. 420. Palceoniscus comptus, Agassiz. Scale, magnified. Marl-slate.—Fig. 421. Pa- 
Imoiiiscus elegans, Sedg. Under surface of scale, magnified. Marl-slate.—Fig. 422. 
Palceoniscus glaphyrus, Ag. Under surface of scale, magnified. Marl-slate.—Fig. 
• 423. Ccelacanthus granulatus, Ag. Granulated surface of scale, magnified. Marl- 
slate. 
Fig. 424. Fig. 425. 
Pygopterus mandibularis, Ag. Marl-slate. Acrolepis Sedgwichii, Ag. Out- 
a. Outside of scale, magnified. &. Un- side of scale, magnified, 
der surface of same. Marl-slate. 
We are indebted to Messrs. Hancock and Howse for the 
discovery in this marl-slate at Midderidge, Durham, of two 
species of Protorosaurus^ a genus of reptiles, one representa¬ 
tive of which, P. Speneri^ has been celebrated ever since the 
year 1810 as characteristic of the Kupfer-schiefer or Permian 
of Thuringia. Professor Huxley informs us that the agree¬ 
ment of the Durham fossil with Hermann von Meyer’s figure 
of the German specimen is most striking. Although the 
head is wanting in all the examples yet found, they clearly 
belong to the Lacertian order, and are therefore of a higher 
grade, than any other vertebrate animal hitherto found fossil 
in a Palaeozoic rock. Remains of Labyrinthodont reptiles 
have also been met with in the same slate near Durham. 
Lower Permian.—The inferior sandstones which lie beneath 
the marl-slate consist of sandstone and sand, separating the 
Magnesian Limestone from the coal, in Yorkshire and Dur¬ 
ham. In some instances, red marl and gypsum have been 
found associated with these beds. They have been classed 
