Lower PaJceozoic Bocks of the South of Scotland. 45 



other suborders of this legion, but also of the important 

 Nassellarian Cystellaria, which are extremely abundant both 

 in recent deposits and in all Tertiary and Mesozoic Radio- 

 larian beds which have as yet been examined. 



With the exception of the Radiolaria very few other 

 organisms can be recognized in the sections of this chert-rock. 

 There are one or two spicules o£ Hexactinellid sponges, 

 readily distinguishable from the detached Beloid spicules by 

 their larger size and distinctive forms, and I have met with a 

 few minute toothed plates and detached denticles, which bear 

 a certain resemblance to the raduUe of naked Molluscs ; there 

 are further nuinerous almond-shaped hollow bodies about "1 

 millim. in length, with imperforate siliceous walls, of whose 

 nature I am quite ignorant. This Ordovician chert may 

 therefore be fairly considered to be due to the accumulation 

 of the tests of Kadiolaria, and is thus a. pure Radiolarian rock, 

 equally as much as the Tertiary beds of Barbados and the 

 Nicobar Islands, which, according to Ha^ckel, correspond to 

 the recent Radiolarian ooze, '' and are certainly of deep-sea 

 origin, having probably been deposited at depths greater than 

 2000 fathoms " *. If the same conclusion is applicable to 

 this fossil chert, it represents, as Prof. H. A. Nicholson f has 

 already pointed out, a true deep-sea deposit in the Paheozoic 

 period, the existence of which in the geological series has of 

 late been disputed. The beds of fine-grained red and green 

 mudstones associated with this chert likewise favour the same 

 view of its origin in deep water. 



Hitherto only a single species of Radiolaria has been 

 described from the entire Palasozoic series, and this was dis- 

 covered by Dr. Rothpletz X in siliceous shale of Upper Silu- 

 rian age at Langenstriegis, in Saxony. This Radiolarian 

 shale, like the Scotch chert, is accompanied by beds with 

 graptolites. It is only since 1876 that Radiolaria were known 

 in any rocks older than Tertiary by the discovery by v. Zittel § 

 of a few forms in the Upper Chalk of Germany ; since then 

 the existence of an abundant and varied Radiolarian fauna in 

 beds of chert and jasper of Lower Cretaceous and Jurassic age 

 lias been proved by Dr. Riist ||, and v. Dunikowski^ has 

 described numerous species in the Lower Lias of the Tyrol. 



• Chall. Report, vol. xviii. pt. i. p. clxix. 



t Trans, Edinb. Geol. Soc. vol. vi. pt. i. p. 56. 



X Zeitschr. d. deutsch. geol. Gesellsch. Bd. xxxii. (1880) p. 447, pi. xxi. 



§ Ibid. Bd. xxviii. (1876) pp. 75-86, pi. ii. 



II * Palaeontographica,' Bd. xxxi., xxxiv. 



% Op. cit. 





