Lower Pahvozoic Hocks of the South of Scotland. 45 



other suborders of this legion, but also of the important 

 NasseUarian Cystelhuia, which are extremely abuiulant both 

 in recent deposits and in all Tertiary and Mesozoic Radio- 

 larian beds which have as yet been examined. 



AVith the exception of the Kadiolaria very few other 

 ore:anisms can be recognized in the sections of this chert-rock. 

 There are one or two spicules of Ilexactinellid sponges, 

 readily distinguishable from the detached IJeloid si)icules by 

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

 few minute toothed j)lates and detached denticles, which bear 

 a certain resemblance to the radulic of naked Molluscs ; there 

 are further numerous almond-shaj^ed hollow bodies about "1 

 niillim. 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 Radiolaria, and is thus a pure Radiolarian rock, 

 equally as much as the Tertiary beds of Barbados and the 

 Kicobar Islands, which, according to Ilaickel, 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 Palaeozoic 

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

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

 niudstones 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 tlie entire Palaeozoic series, and this was dis- 

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

 rian age at Langenstrlegls, 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. Zlttel § 

 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 

 has been proved by Br. Riist ||, and v. Dunlkowskl*[[ 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. ^eol. Gesellsch. Bd. xxxii. (1880) p. 447, pi. xxi. 



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



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



f Op. cit. 



