166 GEOGNOSY AND GEOLOGY. 
are over 15 inches long, and 4 to 6 feet apart, indicating a size of enormous 
dimensions. A discovery of bones of birds in this formation has been 
recently announced. 
Somewhat similar tracks of a different character have been found at 
Hildburghausen. They were sunk in a clay interposed between the strata 
of the variegated sandstone, the sandstone itself exhibiting the cast of the 
track (pl. 41, figs. 31%, 31"). They are batrachoid in their character, and 
were produced in great probability by Labyrinthodonts. The imaginary 
animal which produced these tracks was formerly known as the Chirotherium. 
Some fossils characteristic of the English saliferous system, which belong 
in this place, are Producta horrida (pl. 42, fig. 32); Retepora virgulacea (fig. 
33) ; Terebratula globulina (fig. 34); Terebratula (fig. 35) ; Pecten radialis 
(fig. 36); Avicula grypheoides (fig. 37); Axinus obscurus (fig. 388); 
Retepora flustracea (fig. 39), and a fish, Pale@othrissum macrocephalum 
(fig. 40). 
Oolitic or Jura Formation. The Jura includes all strata between the 
rock salt or new red sandstone and the cretaceous system. The principal 
rock species are an oolitic limestone, clays and marls of tolerably uniform 
color, and a light-colored sandstone. Dolomite occurs in large masses as a 
secondary species. Fossil remains, especially animal, are very abundant, 
both terrestrial and fluviatile. ‘Stone coal occurs in various parts, as also 
carbonate and hydrated oxyde of iron. Three groups may be distinguished. 
a. The Lias (Calcaire a gryphites arquées, Marnes bleues inférieures, 
Terrain liasique). The principal species are clays and. marls with gryphital 
limestone; the clays and marls in the form of shales, loams, clay marls, 
sandy marls, and calcareous marl shales, these mostly penetrated by 
carbonaceous particles, and inclosing nodules of spherosiderite. In the 
Alps the slate clay is transformed into clay slate and calcareous clay 
slate. 
The limestones are more or less pure, often containing iron pyrites and 
grains of earthy chlorite, feetid limestone, marly limestone, and sandy 
limestone. 
Among the accompanying masses are sandstones of various colors and 
grain, which have much similarity to those of the keuper. Subordinate 
masses are gypsum, karstenite, rock salt, carbonaceous strata, anthracite, 
graphite, bituminous shale, drawing slate, and various iron-stones. 
The sandstone, as also an oolitic marly red iron-stone, contains many 
fossils, of which Gryphea cymbium and arcuata are most characteristic and 
important. The thickness of the group varies from that of a few feet to 
whole mountain masses. Ore veins are of rare occurrence and slight 
importance. A few sulphur and saline springs are occasionally met 
with. ) 
This group is distributed in England, Germany, France, and Spain. 
b. Jura Limestone. This is greatly developed in England, and there 
includes all strata lying between the Lias and the so-called Purbeck 
limestone. Oolite is a limestone composed of rounded spheroidal grains of 
various size, somewhat similar in character to a sandstone, and probably 
596 
