24 MONOGRAPH OF DURA DEN. 



spine forms are in many places so numerous that the surface 

 of the rock is hterally covered with them ; the white spear- 

 hke projections contrasting strongly with the fucoid masses in 

 which they are entangled. The plant remains are no less 

 abundant, consisting of stems and branches of trees, and tufts 

 of water-grasses thickly matted together. The stems are 

 generally flattened ; often three to four inches broad ; but 

 the bar-k is so changed by carbonization as to render the 

 application of the microscope of little use. The sedge-like 

 grasses (j'uncites) are slender and jointed, and sometimes 

 several feet in length. Over large areas, and for miles east 

 and west, in every opening of the tilestone bands, the surface 

 of the rock is entirely blackened by these and the other 

 organisms, clearly demonstrating a quiet inland shore-line or 

 marshy lagoon, over which much of the detritus may have 

 been cast by the action of the tides, and in the silt of which 

 several of the grasses may have flourished in situ. Thither 

 would roam the pterogotus, cephalaspis, and other fishes and 

 crustaceans in quest of food, so plentifully supplied by the 

 shrimps, grubs, and other small creatures that lived in the 

 shallows, or there sought a fitting place for the deposition of 

 their spawn among the sea-weeds of the period. 



Resting upon these grey sandstones — the true zone of the 

 cephalaspis and pterogotus — Red Bands of rock succeed (i k) ; 

 and in the lower basin of the Tay and Earn, they consist of three 

 varieties — a fine-grained, a compact gritty, and a conglomerate. 

 "The Clashbennie beds may be taken as the type or representa- 

 tive of the first ; they are always unconformable to the grey 

 sandstones, when seen in conjunction, as in Rossieden and 

 Balruddery, Parkhill and Wormit Bay. This, and the upper 

 series of Dura Den, may be considered as constituting the true 

 zone of the genus holoptycMus, which now for the first time 

 appears in the ascending order of the rocks, along with the 

 phyllolepis and glyptolepis, w^hose scales are very abundant in 

 Clashbennie, Parkhill, and Drumdreel in Stratheden. 



