RIND. 



[ CGI ] 



ROCKS. 



Foramiuifer, with oblique chambers, anil a 

 long sHt-like oritice ou the edge of the last 

 chamber. Aclriatic. (Parker, J. & B., 

 Ann. N. 11. 8. xvi. 1-).) 



RIXD.— This word is used to denote _a 

 structure intermediate between epidennis 

 and bark, — a compound structure consisting 

 of several, or many layers of cells and even 

 of distinct forms of tissue, but not present- 

 ing the characteristic kinds and arrange- 

 ment which occur in true Bark. 



KIVULA'RIA, Koth.— A genus of Oscil- 

 latoriaceie (Confervoid Algae), subdivided 

 by Kiitzing, and restricted to the forms in 

 which there is a distinct manubrmm or 

 elongated cell next to the globular basal 

 cell. As thus defined, it contains only a 

 few aquatic species, the rest being trans- 

 ferred to Physactis, Euactis and allied 

 genera. 



R. anffidosa, Roth. Frond floating, glo- 

 bose, dirty-green ; manubria oblong and 

 curved, or oblong-ovate and abbreviated ; 

 filaments torulose at the base, interruptedly 

 articulated at the apex. E/iff. Bot. 968. 



R. Bonjana, Kg. (PI. 6. tig. 18)_. Frond 

 globose, greenish brown ; the size of a 

 cherry ; manubria large ; sheaths veutricose, 

 colourless, with plaited constrictions ; fila- 

 ments moniliform or interruptedly articu- 

 late, flagelliform. ^.Jiaccida, smaller, fila- 

 ments flaccid, not interrupted. Doubtful 

 species : R. hoinjokles, and R. plana. 



R.plicata, Harv. Frond densely grega- 

 rious, compresso-pUcate, often hollow and 

 ruptured, dark green : filaments spuriously 

 dichotomous, attenuated. 



BiBL. Kiitzing, Sp. Alg. 336 ; Tab. Fliyc. 

 ii. pis. G7, 68 ; Harvey, Br. Alq. 1 ed. 150 ; 

 Hassall, Alg. 262, pi. 64 ; Eng. Bot. Swpp. 

 pi. 2911. 



ROBERTI'NA, D'Orb.— A modification 

 of the Bulimine form of Foraminifera with 

 long oblique chambers, 7-10 in the last 

 whorl, and interdigitating : orifice comma- 

 shaped. Recent and fossil. 



BiBL. Carpenter, For. 196 ; Parker and 

 Jones, Phil. Tr. civ. 375. 



ROBERTSO'NIA, Br. — A genus of 

 Copepodous Entomostraca. R. tenuis, in 

 dredgings. (Brady, Copepod., Ray Soc. ii. 

 25.) 



ROBULI'NA, D'Orb.— A common form 

 of Cristellaria, in which the orifice is trian- 

 gular. 



BiBL. Williamson, Rec. For. 24 {Cris- 

 tellaria) ; Parker and Jones, Ann. N. H. 2. 

 xix. 289. 



ROCCEL'LA, Ach.— A genus of Rama- 

 lodei (Lichenacet)us Lichens)), growing on 

 marine rocks, remarkable as furnishing tho 

 dye called orchil or archil. R. tinctoria, 

 phycopsis, and fusiformis, the British spe- 

 cies, grow only in the extreme south of 

 England. 



BiBL. Hook. Br. Ft. ii. pt. 1. 225; Engl. 

 Bot. pis. 211, 728; Leighton, Lich. Fl. 

 73. 



ROCKS. — Rocks are roughly divided, 

 according to their origin, into an eruptive 

 and a sedimentary series. Again, the erup- 

 tive rocks may be classed in two great 

 groups, the vitreous and the crystalline ; 

 the former being in great part structureless, 

 while the latter consist essentially of cry- 

 stals. A microscopic examination of the 

 vitreous rocks, such as Obsidian, pitchstone, 

 pearlite ifcc, shows, however, that rocks of 

 this class are not wholly devoid of structure, 

 since they almost invariably contain large 

 numbers of minute crystals (microliihs) too 

 small to be referred with certainty to 

 any known mineral species, together with 

 more or less sparsely disseminated crystals 

 of lai'ger size. The microliths, moreover, 

 are frequently disposed in approximately 

 parallel and often tortuous bauds ; while 

 sometimes, bauds of structureless matter, 

 glass of a slightly ditferent colom* and den- 

 sity, are seen to traverse the rock. These 

 bauds, as shown in PI. 42. fig. 8, whether 

 consisting only of glass, or whether I'e pre- 

 sented by lines of microliths, are very cha- 

 racteristic of lava-streams, and are indica- 

 tive of their fusion and flow. Such struc- 

 tures are not always apparent to the naked 

 eye ; and in these cases the microscope -often 

 serves to demonstrate the conditions under 

 which certain rocks have been formed. 



In the examination of the crystalline 

 rocks, which are essentially built up of 

 crystals, frequently of difterent minerals, 

 and pertaining to various crystallographic 

 systems, it becomes necessary to determine 

 their optical characters; and for this pur- 

 pose the employment of polarized light 

 affords the best means of discriminating be- 

 tween them; since, in thin sections of 

 fine-oTained rocks, the application of re- 

 agents to any particular crj-stal or grain is 

 a matter of some difiiculty. Before enter- 

 ing, however, upon the subject of the cry- 

 stalline rocks, it may be well to take a 

 glance at a few of the most characteristic 

 features presented by the vitreous series. 



In the Obsidians, pitchstones, pearlites 



