
Pr, IL. Secr. iii.] DEVONIAN & OLD RED SANDSTONE. 693 
It is interesting fo observe the number of genera and even of species 
common to the Silurian rocks of America and Europe, and the close 
parallelism in their order of appearance. Not a few of the widely 
diffused forms occur in Arctic America, so that a former migration 
along shallow northern waters between the two continents is rendered 
highly probable. Among these common species the following may be 
enumerated as occurring in the Upper Silurian rocks of New York, the 
coasts of Barrow Straits within the Arctic Circle, Britain, and the Baltic 
basin :—Stromatopora concentrica, Halysites catenularia, Favosites gothlandica, 
Orthis elegantula, Airypa reticularis. The graptolites appear to have 
reached their full development and to have waned at corresponding 
stages of the Silurian period on each side of the Atlantic. Among the 
erustacea trilobites were the dominant order, represented in each region 
by a similar succession of genera, and even to some extent of species. 
And as these earlier forms of articulates waned there appeared among 
them about the same epoch in the geological series the eurypterids of the 
Water Lime of New York and of the Ludlow rocks of Shropshire and 
Lanarkshire. 
Asia, &c.—Silurian rocks have been recognized over a large part of 
the surface of the globe. They have been found, for example, running 
through the Cordilleras of South America on the one hand, and among 
the older rocks of the Himalaya chain on the other. The Salt Range of 
the Punjaub contains thick masses of bright red marl with beds of rock- 
salt and gypsum, over which lie purple sandstones and shales containing 
traces of fucoids and annelids and a small brachiopod resembling Obolus. 
These saliferous rocks are probably at least as old as the Silurian period, 
if not older. In the regions of the Northern Punjaub and Kashmere 
traces of Silurian organic remains have been discovered; while in the 
north of Kumaun these fossils have been found in considerable quantities. 
In Australia the existence of the Silurian system has been proved by 
the discovery of a considerable number of characteristic fossils, among 
which are numerous graptolites of the genera Climacograptus, Ceno- 
graptus, Dichograptus, Dicranograptus, Didymograptus, Diplograptus, Mono- 
graptus, Loganograptus, Phyllograptus, Retiolites, and Tetragraptus, which 
occur in the Lower Silurian series of Victoria ; alsomany Upper Silurian 
fossils from New South Wales, including such world-wide species as 
Favosites gothlandica, Heliolites interstinctus, Calymene Blumenbachii, Encri- 
nurus punctatus, Entomis tuberosa, Phacops caudatus, Atrypa reticularis, 
Lepteena sericea, Pentamerus Knightii, P. oblongus, Rhynchonella Wilsont, 
Orthonota amygdalina, Orthoceras bullatum. 
Section III.—Devonian and Old Red Sandstone. 
In Wales and the adjoining counties of England, where the 
typical development of the Silurian system was worked out by 
Murchison, the abundant Silurian marine fauna comes to an abrupt 
close at the base of the red rocks that overlie the Ludlow group. 
From that horizon upwards in the geological series we have to pass 
through some 10,000 feet or more of barren red sandstones and 
marls, until we again encounter a copious marine fauna in the 
Carboniferous Limestone. It is evident that between the dis- 
appearance of the Silurian and the arrival of the Carboniferous 
fauna very great geographical changes occurred over the site of 
