11 



RIOLITE. 



ROCCELLA. 



11 



luxuriant than the nrrounding herbage. They are of two kiniln : 

 ilher ati entire knot of gran is more luxuriant than the rot, or the 

 luxuriant grant grow* in a circle or tbe segment of a circle around a 

 com poratirely barren spot The name of fairy ringt was originally given 

 to thme apoU becttune they were supposed to be the places where tbe 

 little fairies held their nightly revels. Recently a better cause has 

 bean assigned for their origin. They are now known to be those portions 

 of the surface on which a upocie* of fungus has grown, which by dying 

 has afforded nutriment for the grass on the spot; and as the fungus 

 grows in this particular place on account of something favourable to 

 its development, it continues year after year to extend itself beyond 

 the small circular space to which it was originally confined ; but *s the 

 grass in the centre loses the stimulating influence of the decayed 

 fungus, this part becomes comparatively barren, and thus the ring of 

 luxuriant grass keeps on extending for many years, till the earth, no 

 longer affording the circumstances necessary to the development of 

 the fungus, it dies. There are several species of fungus that produce 

 this effect It was first noticed by Dr. Withering aa occurring with 

 the Agarictu oreadet; but the Common Mushroom (A. campatrii), 

 the Gigantic Puff-Ball ( Bovala gigantea), and many others may be seen 

 in the act of forming these circles. It is very probable that most of the 

 large Fungi would form these rings during their growth, provided the 

 entire surface of the earth by which they were surrounded afforded 

 the circumstances necessary to their growth. 



RIOLITE. fZiNi..] 



RIPIDOLITE, a variety of Chlorite. [CHLORITE.] 



RIPPLE-MARK. In geology, the undulations on the surface of 

 many rocks, which resemble the ridges and hollows left on mud and 

 sand by the small waves of water, are thus termed. 



The progress of geological induction has given an unexpected im- 

 portance to the study of these undulations ; for it is now certain that 

 the right understanding of their origin is a very necessary element in 

 reasoning on the deposition of stratified rocks and the displacements 

 of the ancient bed of tbe sea. 



Tbe formation of small ridges and furrows, under the influence of 

 water which ripples or undulates in small waves, may be conveniently 

 witnessed and studied on the shores of comparatively quiet seas, on 

 the margins of lakes, or along the sides and shallow beds of rivers. 

 Tbe ripple-mark thus produced is more or less permanent, according 

 to the nature of the sediments on which it is impressed, and the cir- 

 cumstances which accompany and succeed the withdrawal of the 

 water which formed it 



Loose coarse sand easily receives impressions from the snperfluctuat- 

 ing water, which momentarily change under the varying influences of 

 the waves : muddy sediments are less easily moulded, but the forms 

 are less fleeting. It happens often that on the gradual retreat of the 

 tide from broad muddy surfaces like those in the Bay of Horecambe, 

 or along the shores of the Thames, the small rippling waves of the 

 ebbing tide leave marks sufficiently durable to allow of being inde- 

 finitely preserved, if by any gradual operation some new sediments 

 were gently overlaid. 



A very small ripple leaves its mark on the subjacent sand or mud at 

 only very small depths : larger waves are felt to a greater depth ; and 

 apparently the depth at which ripple-marks are formed maybe judged 

 of, within moderate limits of error, by the breadths of the ripple- 

 marks. Wherever then we find among marine stratified rocks or 

 sediments, of whatever date, undoubted ripple-marks such as shallow 

 waters leave, those deposits contain clear proof of their having been 

 formed at small depths ; and when, as frequently happens, these are 

 seen to be covered by other sediments hundreds or thousands of feet 

 in thickness, the conclusion is just that in those situations the ancient 

 sea-shore underwent a great-subsidence, or the ocean-level experienced 

 gnat rise, after the formation of those now buried ripple-marks. 

 There has been in those situations a change of the level of land or 

 sea. Now, we find ripple-marked strata among the rocks of every 

 geological age. As examples, we mention, among strata lower than 

 the Mountain Limestone, the Fossiliferous Rocks (Qrauwacke) near 

 Kirby Lonsdale, and near Linton in North Devon ; in the sandstones 

 of the Mountain Liinrstone Group, under Penrghent in Yorkshire ; 

 in the sandstone of the Coal-Formation at Elland in Yorkshire; in the 

 sandstones of the New Red-Sandstone-Formation at Storcton near 

 Liverpool ; in tbe sandstones of the Oolitic Rocks near Scarborough 

 and near Stamford ; in the Wealden deposits at Horsted. 



In most cases ripple-mark is found on sandstones or indurated clays 



nnograin "d frequent lamination, and it i* most distinct on sur- 

 CMSS where a change of deposit happens, as where sandstones alternate 

 with thin clay partings. Rarely, as in the Storeton quarries, impri- 

 sions of quadrupeds accompany the ripple-mark ; and it is even 

 thought that marks of rain are prenerve.1 thereon. 



(Babbage, Mnlh /IriJyaeater Tnatuc ; Playfair, Uultonian Theory; 

 LT.II, l'*l*<i "f '-"loyy : De U Beche, Theoretical Rttearehtt.) ' 



i. US. [P<Boiu>roDA.1 



Itl'SSOA, M. De Fmninville s name for a g^nns of Oasteropodous 

 MtUmtea, founded on some small shells observe.! by M. Risno of Nice 

 and described by M. Umnarest in 1814 in tbe 'Nouveau Bulletin de 

 la Hociet/- Hhilomathiq.i*. 1 



Lamarrk placed the few specie* known to him among the Mrlanur 

 but without distinction. Delle Chiaje uiadc known the animal struc- 



ture of a Mediterranean species in his ' Memoirs on the Invertebrate 

 of the Neapolitan Sea ;' and Pbilippi recorded its generic characters 

 in his ' Kuumeratio Mollnsoorum Siciliw,' from observations made upon 

 two other Mediterranean species. 



The animal has a subtriangular foot, truncated anteriorly, pointed 

 posteriorly. Head proboscidiform, with a subulate tentacle on each 

 side, at the external base of which the eye is placed on a little con- 

 vexity ; mouth prolonged into a short and truncated proboscis. 



Shell elongated, turriculate, sometimes short and subglobulor; 

 aperture oval, semilunar, subcanaliculate, having the right lip 

 thickened, and nearly always projecting forwards, and arched longi- 

 tudinally ; operculum horny, closing the aperture exactly. 



M. De Illainvillo divides the genus into the following sections; 



A. Turriculatcd and Ribbed. Ex. II. acuta. 



B. SubturricuUted and Ribbed. Ex. R. cottata. 



C. Subturriculated ; perfectly smooth. Ex. R. hyalina. 



D. Subglobular. Ex. R. cancellaia. 



The same divisions are adopted by M. Rang. 



There are about 70 recent species, which are very generally dis- 

 tributed, but are most abundant in the north temperate zone. They 

 are found in North America, the West Indies, Norway, the Mediter- 

 ranean, the Caspian, and in other seas. Messrs. Forbes and Uanley 

 describe 27 species as inhabitants of the British seas. Hydrobia 

 Lyncera, Nematura, and Jtfreysia are sub-genera. 



One hundred species have been described as fossil. They arc found 

 in the Permian Rocks of Great Britain and France. 



RIVER-HORSE. [HIPPOPOTAMUS.] 



ROACH. [LEUCISCUS.] 



ROAN-TREE. [Pinna.] 



ROBIN-REDBREAST. [ERTTIIACA.] 



ROBIN-HUSS. [SQUALID*.] 



ROBI'NIA, a genus of Plants belonging to the natural order 

 Legnminome, named in commemoration of John Robin, a botanist in 

 the time of Henry IV. of France. This genus is known by having an 

 inferior perianth ; teeth of calyx 5, lanceolate, two upper ones shorter 

 and approximate ; corolla papilionaceous ; ovary with from 16 to 20 

 ovules; style bearded in front, and legume sub-sessile and many- 

 seeded. They are North American trees, bearing nodding racemes of 

 white or rose-coloured flowers. The genus Robinia formerly compre- 

 hended the plants now included under Caragana, from which it is dis- 

 tinguished by its long gibbous legume and unequally pinnate leaves. 



The best known species of Robinia is the R. pitiulacacia, the 

 Bastard or False Acacia. It has stipular prickles, with loose pen- 

 dulous racemes of white sweet-smelling flowers, which, as well as the 

 legumes, are smooth. This tree, which is now so well known, was first 

 grown in Europe by Vespasian Robin, the son of the botanist, after 

 whom the genus was named, in the Jardin-des-Plantes at Paris. 



It has always been known in America as affording an exceedingly 

 hard and durable wood. It is there used for making posts, and occa- 

 sionally trees are found largo enough to be employed in ship-building; 

 but its greatest consumption is for making trenails, by which the 

 timbers of ships are fastened together, and for this purpose large 

 quantities are used in the royal dockyard at Plymouth, which are 

 imported from America. 



Cattle are fond of the young shooU, and on this account it has 

 been recommended to bo cultivated as forage. 



The roots and other ports of the plant, like many of its order 

 (Leguminotir), contain a saccharine principle, which accounts for the 

 nutritive properties of the leaves. In St. Domingo the flowers are 

 used for making a distilled liquor, which is said to be very delicious. 

 It folds up its leaves at the approach of night 



There are two other species frequently cultivated in this country, 

 R. viicota, the Clammy Robinia, and R. Itupida, the Hairy Robinia, or 

 Rose-Acacia. The former is characterised by the sticky secretion with 

 which it is covered, and which has been discovered to possess a 

 peculiar vegetable principle. The latter, which is the smallest of 

 the three species here mentioned, has very large flowers, and forms 

 a very ornamental shrub when grown on on espalier rail or against 

 a wall. 



ROCAMBOLE. [ALLIDM.] 



ROCCELLA, a genus of Plants belonging to the family of Lichens. 

 The species are used in dyeing, and are popularly called Orchil, or 

 Archil. This name is derived from the Oricello of the Italians or the 

 Spanish Orcbell*. It is often corrupted in commerce into Rochilla- 

 Weed. Several species of Lichens are employed for the same purpose, 

 which are distinguished according to the country whence they are 

 imported, and also by manufacturers into Weed and Moss, the former 

 name being applied to the Filiform Lichens of botanists belonging to 

 tbe genus Soceella, to be treated of here, whilst the terms Moss and 

 Rook-Moss are applied to the Crustaceous Lichens belonging to the 

 genus Leeanora, which include the Cudbear and I'arelle of dyers. 

 [PARKU.A.] 



The character of tbe genus Hoccclla is as follows: Timlin* coriaceo- 

 cartuaginous, rounded or plane, branched or laciueated ; apotbecia 

 orbicular, adnate with the thallus ; the disc coloured, plano-convex, 

 with a border at length thickened and elevated, formed of the thallus, 

 and covering a siibK-ntiforui black compact pulverulent powder, con- 

 cealed within the substance of the thallus. 



