deposits are the oldest yet discovered. In Styria and Bohemia 
important beds of oolitic hematite and siderite are interstratified with 
the ordinary greywackes and shales. Occasionally sheets of various 
eruptive rocks (felsites, diabases, diorites, &c.) occur contempor- 
aneously imbedded in the Silurian rocks (N. Wales, &e.), and with 
their associated tuffs represent the volcanic ejections of the time. 
As a rule Silurian rocks have suffered from subsequent geological 
revolutions, so that they now appear inclined, folded, contorted, 
broken, and cleaved, sometimes even metamorphosed into crystalline 
schists. In certain regions, however (Basin of the Baltic, New York, 
&c.), they still remain nearly in their original undisturbed positions. 
Lire.—The general aspect of the life of the Silurian period so far 
as it has been preserved to us, may be gathered from the followimg 
summary published by Dr. Bigsby in 1868—plants 82 species ; amor- 
hozoa 186; foraminifera 25; ecelenterata 507; echinodermata 500 ; 
annelida 154; cirripedes 8; trilobita 1611; entomostraca 318; 
polyzoa 441; brachiopoda 1650, monomyaria 168; dimyaria 541; 
heteropoda 358; gasteropoda 895; cephalopoda 1454; pisces 37; 
class uncertain 12; total 8897 species. M. Barrande in 1872 pub- 
lished another census in which some variations are made in the 
proportions of this table, the total number of species being raised to 
10,074. 
The plants as yet recovered are chiefly fucoids. In many cases 
they occur as mere impressions which may sometimes be not of 
vegetable origin at all, but casts of the trails or burrows of worms, We. 
Among the most abundant genera are Buthotrephis, Arthrophycus, 
Palxophycus, and Nematophycus (Carruth.), the latter having appa- 
rently been a gigantic form somewhat like the living arborescent 
Lessonia. But in the Upper Silurian rocks beautifully preserved 
sea-weeds like the living Gelidiwm or Plocamiwm occur, such as the 
Chondrites verisimilis (Salt.) of the Ludlow rocks of Edinburgh- 
shire. ‘Traces, however, of a higher vegetation have been discovered 
which are of special interest as being the earliest known remains of a 
land flora. Many years ago certain minute bodies found in the 
Ludlow bone-bed were regarded as lycopodiaceous spore-cases, but 
some doubt has been cast on their organic grade. More recently, 
however, Dr. Hicks has obtained from the Denbighshire grits of 
N. Wales other spores probably lycopodiaceous.! True lycopods 
(Sagenaria) have been met with in the Upper Silurian rocks of 
Bohemia and a supposed fern (Hopteris Andegaveris) in the Lower 
Silurian slaty schists of Angers containing Calymene Tristan From 
the Clinton limestone of Ohio portion of a lepidodendroid tree 
(Glyptodendron Hatonense) has been obtained, The Cincinnati group 
of strata has also yielded a Sphenophyllum. From the meagre 
evidence as yet collected, it would appear that the land of the 
1 Q. J. Geol. Soc, 1881, p. 482. 
* G. De Saporta, Comptes rendus, Ixxxv. (1877), No. 10. M. Meunier-Chalmas has 
suggested that this supposed fern is a crystallization of pyrites—a view taken also by 
Mr. Carruthers. 

ee 
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662 STRATIGRAPHICAL GEOLOGY. [Boos VI. 

