42 DE. G. J. HINDE ON THE EADIOLARIA IN THE [Feb. 1 89 9, 



silica in the rock. This seems to be accounted for by the greater 

 quantity of very fine clay or silicate of alumina that has taken the 

 place of the silica. The radiolaria in the rock, judging from the 

 weathered-out forms, are fairly well preserved, but in the micro- 

 scopic sections they are obscured by the aluminous groundmass, 

 which cannot be eliminated as in the case of the calcium carbonate in 

 the siliceous limestones. Hence their generic and specific characters 

 cannot be determined with precision, but there is no reason to doubt 

 their similarity to the forms in the intervening siliceous limestones. 



(d) The Volcanic TufiPs with Radiolaria. 



Some of the beds at Tamworth associated with the radiolarian 

 siliceous limestones and claystones appear to be made up mainly of 

 volcanic detritus, judging from the characters shown in microscopic 

 sections. The specimens examined bear the numbers 240 a i, 243 2, 

 249 A 1, 257 A, 380 d-e, and 387 n. The rocks are mostly of a bluish 

 tint ; they may be scratched with a penknife, and readily effervesce in 

 acid. The outer surface weathers to a rusty brownish crust of fine 

 and coarse granular materials. Under the microscope the rock is 

 seen to consist of irregular fragments of tuff, lapilli, and ash of 

 different degrees of fineness ; in a coarse example the fragments 

 range up to 2*5 mm. in diameter. Some fragments are vesicular, 

 and the vesicles are regularly oval and often filled with a greenish 

 mineral. As they are of about the same size as radiolarian casts, they 

 might easily be mistaken for these organisms. The base or ground- 

 mass of the tufi*-rock is calcite, which cements the fragments together. 

 Scattered sparsely between the tuff-fragments and, like them, 

 embedded in the calcitic base there are a few radiolaria, which 

 can hardly be seen until the calcite has been removed by acid, in the 

 same way as in the radiolarian limestones. The forms in the tuff- 

 rocks are generally well preserved ; the lattice-structure of the outer 

 and inner tests and the radial spines can be distinguished, and they 

 still retain the colloid silica of the test. In exceptional instances 

 the interior of the test has been infilled with colloid silica, but more 

 usually with calcite. Owing to their isolated occurrence, the syste- 

 matic characters of these tuff radiolaria can be better ascertained 

 than in the forms in the limestones, and a majority of those described 

 and figured in the following pages are from a single hand-specimen 

 of tuff (387 d), in which the fragments are coarser than the 

 average. 



III. Description oe the Eadtolaeia. 



The descriptions and figures which follow have in all cases been 

 taken from the radiolaria seen by transmitted light, in the etched 

 microscopic sections of the dark siliceous limestones and the volcanic 

 tuffs of the Tamworth series. It has not been found practicable 

 to figure the forms weathered out on the surface of the rocks, or 

 partially set free by acid. In the etched sections the outer cortical 



