Yol. 55.] oisr PALEOZOIC eadiolarian" eocks in 1^. s. WALES. 27 



Sections on the Great ]S"orthern Railway near 

 Tamworth. 



In cuttings of the Great Northern Railway, along the course of 

 the valley of the Cockburn River, south-east and east of Tamworth, 

 sections of the radiolarian shales and tuffs are well shown. The 

 first cutting east of Tamworth, near the 188-mile post, is in laminated 

 radiolarian shales dipping south 25° west at 50°; beyond this, other 

 cuttings, with extended interspaces where the rocks are not shown, 

 reach nearly to the 190-mile post, and at a short distance from 

 this point the granite comes in. The position of the cuttings is 

 shown in the accompanying map (PL II), and a section, drawn to 

 scale, has been prepared, which illustrates the character of the beds 

 passed through in the cuttings for a distance of 1 mile 20 chains 

 (PL TV). The radiolarian rocks are almost wholly clay-shales and 

 mudstones, varying in tint from brownish-grey and olive-brown to 

 dark grey and black. They are usually soft and finely laminated, 

 and for the most part they occur as thin bauds from 2-5 to 15 

 or even 30 cm. thick, which alternate between beds of tuff of 

 the same or greater thickness. The shales sometimes pass into 

 chert in contact with the tuffs, and cherty masses occasionally occur, 

 enclosed within the tuff-beds. The shales contain radiolaria in 

 great abundance, and they can be distinguished even without a 

 lens. 



On at least four horizons in the railw^ay-cuttings, there are 

 abundant plant-remains associated with radiolaria in the shales. 

 On two horizons the plants are certainly Le]Didodendron australe, on 

 another the Knorria condition of the same plant, and on the fourth 

 horizon probably Knorria also. These plant-remains are not 

 merely isolated specimens, for they are fairly numerous on the 

 horizons where they occur, from three to ten specimens appearing in 

 every square foot of the bed. The occurrence of these plant-beds, on 

 the hypothesis that they were due to occasional specimens drifted 

 far out to sea and then waterlogged, does not therefore apply. In 

 two places also along the line of railway we observed clear evidence 

 of ripple-marks in the radiolarian rocks. 



' The submarine acidic tuffs exposed in the railway-cuttings are, 

 as a rule, evenly bedded, and sometimes finely laminated. Some 

 beds are of considerable thickness, others very thin. The tuffs are 

 greenish-grey at a depth, while at the surface they weather into a 

 reddish-brown rock with separation of white veins (of magnetite ?). 

 In weathering also the tuffs not infrequently assume the form of 

 rude spheroids. Pebbles of eruptive rock up to 7'5 cm. in diameter 

 sometimes occur in these tuff-beds, and rarely also they contain 

 impressions of plants. 



Though, as a rule, the tuff-beds are regularly and evenly inter- 

 bedded with the radiolarian clay-shales, instances are not infrequent 

 where these rocks are confusedly intermingled together. An example 

 of this is seen in the accompanying reproduction of a photograph 



