46 MONOGRAPH OF DURA DEN. 



more precise. Along the line of our geological section, from the 

 azoic members of the primary series to the upper fossiliferous 

 strata of the Devonian system, there are at least three well- 

 characterized suites of rockS;, with their correlative enclosed 

 organic remains. The lower grey sandstones represent a zone 

 of life when huge crustacean types prevailed in the seas and 

 estuaries of the district, in the remarkable forms of pterogotus, 

 pterichthys, cephalaspis, coccosteus, himantopterus, and stylon- 

 urus. Next appeared the thick, shining-scaled sauroids and 

 calacanths, represented by dipterus, osteolepis, cheiracanthus, 

 dendrodus, acanthodi, and other genera of cartilaginous fishes. 

 The highest zone of the period embraces the red and yellow 

 sandstones of Clashbennie and Dura Den, when the holoptychius 

 family appears for the first time in countless numbers and 

 gigantic forms, and accompanied by congeners of strong affini- 

 ties in size and scaly armature, as the platygnathus, glypto- 

 pomus, glyptolepis, phyllolepis, diplopterus, and now, as in this 

 work for the first time figured and described, the GlyptolcBmus 

 and the Plmnero'pleuron. The grand epos of organic life 

 immediately succeeds, ushered in by a vast profusion of plants, 

 countless multitudes of molluscs, an extraordinary increase of 

 fishes which " the waters brought forth abundantly ;" and now 

 also, as appears to be clearly established, the higher reptihan 

 structure of organization is brought upon the scene. Thus the 

 tribes and products of the carboniferous age have their repre- 

 sentatives among the plants in immense varieties of ferns, 

 lycopodiums, calamites, sigillaria, lepidodendrons, coniferse, and 

 cycadectD ; among the shell forms are the encrinites, producti, 

 inocerami, pectens, mytilli, orthes, spirifers, bellerophons, go- 

 uiatites, nautili, and orthoceratites ; among the fishes are the 

 well-marked amblypterus, palaeoniscus, gyracanthus, cteracan- 

 thus, eurypterus, and megalichthys ; and all of whose combined 

 remains now constitute our rich deposits of coals, ironstone 

 l)ands, and lofty mountains of limestone. 



Dura Den stands on the verge of the two gi'eat epochs — 



