| Locality 2. | Relative Abundance of Radiolaria. | ||||
|---|---|---|---|---|---|
| 338. | Tr. Atl. | 1990 | 36.3 | gl. oz. | D f" |
| 340. | Tr. " | 1500 | 37.6 | pt. oz. | E very few |
| 341. | Tr. " | 1475 | 38.2 | pt. oz. | E very" |
| 342. | Tr. " | 1445 | 37.5 | pt. oz. | D few |
| 343. | Tr. " | 425 | 40.3 | volc. s. | E very few |
| 344. | Tr. " | 420 | ... | volc. s. | E very" |
| 345. | Tr. " | 2010 | 36.8 | gl. oz. | D few |
| 346. | Tr. " | 2350 | 34.0 | gl. oz. | C many |
| 347. | Tr. " | 2250 | 36.2 | gl. oz. | B numerous |
| 348. | Tr. " | (2450) | ... | (Pelag.) | B num" |
| 349. | Tr. " | ... | ... | (Pelag.) | B num" |
| 350. | Tr. " | ... | ... | (Pelag.) | B num" |
| 351. | Tr. " | ... | ... | (Pelag.) | B num" |
| 352. | Tr. " | ... | ... | (Pelag.) | B num" |
| 353. | N. Atl. | 2965 | 37.6 | r. cl. | C many |
| 354. | N. " | 1675 | 37.8 | gl. oz. | D few |
 | Date. | Latitude and Longitude. | Nearest Land. | ||||||
|---|---|---|---|---|---|---|---|---|---|
| 1876. | |||||||||
| 338. | Mar. | 21 | 21° | 15′ S., | 14° | 2′ W. | (Ocean). | ||
| 340. | F" | 24 | 14° | 33′ S., | 13° | 42′ W. | Ocean |  | W. of St. Helena. |
| 341. | F" | 25 | 12° | 16′ S., | 13° | 44′ W. | Ocean | ||
| 342. | F" | 26 | 9° | 43′ S., | 13° | 51′ W. | Ocean | ||
| 343. | F" | 27 | 8° | 3′ S., | 14° | 27′ W. | Ascension Island. | ||
| 344. | April | 3 | 7° | 54′ S., | 14° | 28′ W. | Ascension Island. | ||
| 345. | F" | 4 | 5° | 45′ S., | 14° | 25′ W. | Ocean |  | Tropical Atlantic, between Ascension and Sierra Leone. |
| 346. | F" | 6 | 2° | 42′ S., | 14° | 41′ W. | Ocean | ||
| 347. | F" | 7 | 0° | 15′ S., | 14° | 25′ W. | Ocean | ||
| 348. | F" | 9 | 3° | 10′ N., | 14° | 51′ W. | Ocean | ||
| 349. | F" | 10 | 5° | 28′ N., | 14° | 38′ W. | Ocean | ||
| 350. | F" | 11 | 7° | 33′ N., | 15° | 16′ W. | W. of Sierra Leone. | ||
| 351. | F" | 12 | 9° | 9′ N., | 16° | 41′ W. | W. of Sierra Leone. | ||
| 352. | F" | 13 | 10° | 55′ N., | 17° | 46′ W. | W. of Sierra Leone. | ||
| 353. | May | 3 | 26° | 21′ N., | 33° | 37′ W. | W. of Canary Islands. | ||
| 354. | F" | 6 | 32° | 41′ N., | 36° | 6′ W. | S. of Azores. | ||
CHAPTER X.—GEOGRAPHICAL DISTRIBUTION.
(§§ 241-250.)
241. Historical Distribution.—Radiolaria are found fossil in all the more important groups of the sedimentary rocks of the earth's crust. Whilst a few years ago their well-preserved siliceous skeletons were only known in considerable quantity from Cainozoic marls (§ [242]), very many Spumellaria and Nassellaria have recently been found in Mesozoic and a few in Palæozoic strata. By the aid of improved modern methods of investigation (especially by the preparation of thin sections of very hard rocks) it has been shown that many hard siliceous minerals, especially cryptocrystalline quartz, contain numerous well-preserved Radiolaria, and sometimes are mainly composed of closely compacted masses of such siliceous shells; of this kind are many quartzites of the Jura (§ [243]). These Jurassic quartzes (Switzerland), as well as the Tertiary marls (Barbados) and clays (Nicobar Islands), are to be regarded as "fossil Radiolarian ooze" (§ [237]). Dense masses of compressed Spumellaria and Nassellaria form the principal part of these rocks. Isolated or in smaller quantities, fossil Polycystina, belonging to different families of Spumellaria and Nassellaria, also occur in in other rocks, and even in some of Palæozoic origin. Since specimens have also been recently found both in Silurian and Cambrian strata, it may be stated that as regards their historical distribution, Radiolaria occur in all fossiliferous sedimentary deposits, from the oldest to those of the present time.
242. Cainozoic Radiolaria.—The great majority of fossil Radiolaria which have hitherto been described, belong to the Cainozoic or Tertiary period, and in fact, to its middle portion, the Miocene period. At this period the richest and most important of all the Radiolarian formations were deposited, such as the pure "Polycystine marl" of Barbados (see note A), also that of Grotte in Sicily (see note B), and the clay of the Nicobar Islands (see note C). Besides the above-mentioned deposits, which may be designated "pure" fossil Radiolarian ooze, many deposits containing these organisms have recently been discovered in widely separated parts of the earth, partly of the nature of tripoli or marl, partly resembling clay. Among these may be mentioned in the first place many coasts and islands of the Mediterranean, both on the south coast of Europe (Sicily, Calabria, Greece), and the north coast of Africa (from Oran to Tripoli). The extensive layers of tripoli which are found in these Mediterranean Tertiary mountains belong to the upper Miocene (Tortona stage), and consist partly of marl rich in calcareous matter, and resembling chalk, partly passing over into plastic clay or "Kieselguhr" (§ [246]). The quantity of Radiolaria contained varies, and is more conspicuous the fewer the calcareous shells of Foraminifera present. Similar Tertiary Polycystine formations occur in some parts of America (see note D); probably they have a very wide distribution. In their general morphological characters, the Tertiary Spumellaria and Nassellaria are related to those forms which are found in the recent Radiolarian ooze of the depths of the Pacific, especially to the species which are characteristic of the Challenger Stations 225, 226, 265 and 268. Many living genera and families (e.g., most Larcoidea and Stephoidea) have not yet been found in the Tertiary formations.
A. The famous Polycystine marl of Barbados in the Antilles, which Robert Schomburgk discovered forty years ago, belongs to the Miocene formation, and is the richest and best known of all the important Radiolarian deposits (see L. N. [16], pp. 5-8). After Ehrenberg had published in December 1846 the first preliminary communication regarding its composition out of masses of well-preserved Polycystina, he was able in the following year to describe no less than 282 species from it; he distributed these in 44 genera and 7 families (L. N. [4], 1847, p. 54). In the year 1854 Ehrenberg published figures of 33 species in his Mikrogeologie (L. N. [6], Taf. xxxvi.); but it was only in 1873 that he published descriptions of 265 species (Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, Jan. 30, pp. 213-263). Finally there followed in 1875 his Fortsetzung der Mikrogeologischen Studien, mit specieller Rücksicht auf den Polycystinen-Mergel von Barbados (L. N. [25]). On the thirty plates which accompany this the last work of Ehrenberg, 282 species are figured and named, of which 54 are Spumellaria (13 Sphæroidea, 8 Prunoidea, 33 Discoidea), and 228 Nassellaria (2 Stephoidea, 38 Spyroidea, and 188 Cyrtoidea). The fourth section of this memoir contains a survey of the Polycystine formation of Barbados (pp. 106-115), and the fifth section the special description of a large specimen of rock from Mount Hillaby in Barbados (see also L. N. [28], p. 117, and L. N. [41], pp. 476-478). The account given by Ehrenberg of the Polycystina of Barbados is in many respects very incomplete, and very far from exhausting this rich mine of remarkable forms. This may be readily seen from the twenty-five plates of figures of Polycystins in the Barbados Chalk Deposit published by Bury in 1862 (L. N. [17]). The number of species here figured (140 to 142) is about half of those given by Ehrenberg; and there are among them numerous generic types, some of great interest, which were entirely overlooked by the latter; e.g. Saturnalis (Sphæroidea), Cannartidium (Prunoidea), Tympanidium (Stephoidea), Cinclopyramis (Cyrtoidea), &c. Finally, Ehrenberg always (until 1875) ignored Bury's atlas, which had been published thirteen years ago and was quite accessible to him. How different were the contents of the two works may easily be seen from the following abstract.
Comparative View of the Species of Fossil Radiolaria from Barbados made known by the figures of Bury in 1862 and of Ehrenberg in 1875.
| Legion. | Order. | Bury. | Ehrenberg. | Total. | |
|---|---|---|---|---|---|
| II. Legion Spumellaria (Peripylea). |  | 1. Sphæroidea | 16 | 13 | 29 |
| 2. Prunoidea | 10 | 8 | 18 | ||
| 3. Discoidea | 37 | 33 | 70 | ||
| II. Legion Nassellaria (Monopylea). | | 4. Stephoidea | 5 | 2 | 7 |
| 5. Spyroidea | 13 | 38 | 51 | ||
| 6. Cyrtoidea | 60 | 188 | 248 | ||
| Total, | 141 | 282 | 423 | ||
| Legion. | Order. | Bury. | Ehrenberg. | Total. |
|---|---|---|---|---|
| II. Legion Spumellaria (Peripylea). | 1. Sphæroidea | 16 | 13 | 29 |
| 2. Prunoidea | 10 | 8 | 18 | |
| 3. Discoidea | 37 | 33 | 70 | |
| II. Legion Nassellaria (Monopylea). | 4. Stephoidea | 5 | 2 | 7 |
| 5. Spyroidea | 13 | 38 | 51 | |
| 6. Cyrtoidea | 60 | 188 | 248 | |
| Total, | 141 | 282 | 423 | |