156 C. I). WALCOTT — DISCOVERY OF SILURIAN VERTEBRATES. 



Page, 

 a network of the casts of the borings. On the southern side of 

 the Arkansas river, two miles south of the section, there were 

 found in a stratum 20 feet above the Algonkian rocks numerous 

 laniellibranchs, a few gasteropods, and numerous fragments of 

 the plates and scales of placo-ganoid fishes. , 



c — Reddish-brown sandy shales that arc partially calcareous in some 



layers 7 



Fossils. — Fish plates in great abundance and, in the calcareous 



layers. Orihoceras multicameratum, Hall (?), BeyricMa (like />'. 



fabulites, Conrad), and several species of lamellibranchs (sec 



list, page 158). 



d — Massively bedded gray and reddish sandstone, with thin irregular 



beds of reddish-brown sandy shale in the lower portion 20 



Fossils. — Fish plates and scales of fish are numerous in the 

 lower portion and also in a reddish-brown capping of the mas- 

 sive bed in which the Harding quarry is located. The supposed 

 chorda] sheaths occur scattered through this bed and also more 

 rarely in /», c and < . 



» — Fine-grained argillaceo-arenaceous shale .'! 



< rray and buff sandstone 7 



— 10 

 / — Coarse purplish-tinted sandstone in several layers, with gray layers 



a hove 11 



Fossils. — Plates and scales of fish. 



Total sandsti me 86 



Observations on thi Harding Sandstone Series. — The Lower bed is a shore- 

 line deposit following the advance of the sea upon the land; it is 

 formed of coarse -rains of quartz and small quartz pebbles imbedded 

 in a fine arenaceous matrix. The succeeding layers of sandstone have 

 more or less calcareous matter in the matrix. Their contained aceph- 

 alous shells, drift-worn plates and scales of fishes, and the vast num- 

 ber of casts of annelid borings, all prove the littoral origin of the 

 sediments. The fish plates and scales are scattered more or Less 

 throughout the beds, but they are very abundant in four principal 

 /ones, viz, c of the section : near the base, and again near the summit 

 of d; ami ai the summit of ,. in e they are commingled with re- 

 mains of Orthocei-as and with acephalous mollusks and gasteropods. 

 The closing deposit of the sandstone series is formed of a coarse drifted 

 sand, containing numerous fragments of larger fish plates than those 

 below. The change to the succeeding shaly beds is abrupt, and appar- 

 ently due to the deepening of the water and the cessation of arena- 

 ceous deposits. 



'_'. Red and purple tine-grained argillaceo-arenaceous shale 2-4 



Fossils. — Rolled and worn fragments of fish plates occur in 

 the lower portion. 

 :!. Graj silicious magnesian limestone, somewhat ferruginous in the 

 lower portion. Locally, this decomposes to a reddish, friable rock 

 and soil : the entire mass above 25 feet from the base weathers into 

 rough, irregular cliffs with numerous shallow caverns and holes of 

 various sizes and forms 170 



