general characterizes these products may be accounted for by the pressure of the superincumbent water; but, as the same effect might result from the weight of a considerable bed of tuff or scoriæ, the occasional occurrence of compact lava beds, even amongst subaërial volcanos, need not so much surprise us. When, therefore, I remarked, that no genuine basalt had, to my knowledge, been found amongst the lavas of those volcanos which are at present in activity, and that their ejections do not appear to exhibit the same columnar arrangement which belongs to the igneous products of an earlier age, I by no means meant to deny the possibility of such occurring, but only to awaken attention to the point, in the hope that other observers might ascertain its truth or falsehood. The distinction, however, which I have attempted to maintain* between that irregular prismatic structure, which is the mere result of contraction, and is so well exhibited in the modern lava of Niedermennig, and that of articulated columns which is derived apparently from the mutual pressure of spheroidal concretions, be it true or false, will not be overturned by the observation, that in some instances a void space exists between the respective columns of the last mentioned kind. For it is evident, that the compression which converted the spheres into polygons would take place whilst the material was yet soft, and that a further degree of shrinking might therefore be expected to occur, before it became perfectly cold. This, I conceive, furnishes a sufficient reply to Mr Scrope's objection in page 149 of his Memoir on Central France, especially when backed by the ingenious observations of Mr Gregory Watt, published in the Philosophical Transactions for 1808, from which it appears, that, after a melted mass has become in a great degree consolidated, chemical affinities continue to develop themselves, and crystalline arrangements to take place. But I trust I have already said enough to prevent misconstruction, in case I should in any subsequent treatise, in which it might be inconvenient to introduce remarks of a controversial nature, think proper to adhere to those views which I had taken • See Description of Volcanos, p. 49. and 422. up previously to the publication of the writings I have been obuiged here to allude to. If I stood alone in these opinions, I might perhaps bow to the authority of individuals more exclusively devoted to the study of geology than myself, who have arrived at opposite conclusions; but when I see the best naturalists divided, and even some of those who adopt, to a certain degree, the views proposed to be substituted for the, diluvial theory, compelled to call in the assistance of something of the same kind to explain certain refractory phenomena, I think it best for the present to retain my original views on these points, which are still espoused by the individuals who first gave them currency in this country, and which, whether true or false, serve at least to convey a clear conception of the relation existing between the volcanic products of the districts I have described. I ought not, however, to conclude this long epistle, without bearing my humble testimony to the merits of the work which first induced me to address you, and expressing the satisfaction I have experienced in perusing a treatise on Geology, which, unlike some of those which preceded it, is distinguished no less for the number and general accuracy of its details, than for the philosophical spirit in which it is conceived. I am quite prepared to admit, that the accounting for all the phenomena exhibited on the earth's surface, not only consistently with the present laws of nature (for on that point I suppose we are all agreed), but also without having recourse to any operations but those we are eye-witnesses of, constitutes in a manner the beau ideal at which our researches should aim, and would, if successful, elevate geology to the rank of the exact sciences. But we must be on our guard, nevertheless, not to be led away by the charm of simplicity, so as to overlook the difficulties which seem at present to stand in the way of such an explanation, and imagine the object within our reach, when it is seen only perhaps in distant and doubtful perspective. Whether, too, the modifications which the author has chosen to introduce in the Huttonian Theory be an improvement in it, seems to me questionable; but be that as it may, the surviving supporters of that hypothesis will welcome with acclamation a disciple who has maintained, with so much skill and research, the leading positions of their system; and I am sure that, if its illustrious founder were now alive, he would testify as much delight as at the discovery of the granite dikes of Glen Tilt, when he saw the conclusions, which he had deduced from a more imperfect survey of geological phenomena, rendered popular in the south by the ingenious reasonings of one, whom, though he cannot certainly be said to belong to the Oxford School of Geology," as it is somewhere called, Alma Mater will, I am sure, be always proud to number among her sons, On the Characters and Affinities of certain Genera, chiefly belonging to the Flora Peruviana. By Mr DAVID DON, Librarian to the Linnean Society, Member of the Imperial Academy Naturæ Curiosorum, of the Royal Botanical Society of Ratisbon, and of the Wernerian Society of Edinburgh, &c. (Concluded from p. 122.) THESE QUILLAJA and KAGENECKIA. HESE genera, together with Vauquelinia, I consider as constituting a small family, differing essentially both from Rosacea and Spiraeaceae in their erect ovula, and from the latter, also, in the valvular æstivation of their calyx. The habit of the plants composing it is likewise abundantly different, and they are mostly inhabitants of the southern hemisphere. This family may be termed Quillajea and it may be characterised as fol lows: 8 11 CALYX 5-fidus, æstivatione valvatus. PETALA 5, laciniis calycinis alterna; quandoque nulla. STAMINA definitè numerosa (10 v. 15) calyci inserta : antheræ biloculares. PISTILLUM: Ovaria 5, basi connata, unilocularia: ovula numerosa, erecta: styli 5: stigmata totidem, unilateralia, papillosa. FRUCTUS: folliculi 5, in circulum digesti, basi connati. SEMINA duplici ordine suturæ folliculorum internæ inserta, adscendentia, apice alata: umbilico basilari: testa simplex, membranacea: albumen nullum. EMBRYO erectus! "cotyledones foliaceae, contrariè convolutae: radicula cotyledonibus brevior, teres, umbilico proxima. Arbores (præcipuè Amer. Austr.) Folia allerna indivisa. Stipulæ minimæ, caduce. Flores terminales, dioici. QUILLAJA, Mol. Juss. SMEGMADERMOS, Ruiz et Pavon. SMEGMARIA, Wild. Calyx 5-fidus: laciniis ovatis, obtusiusculis, crassis, densè tomentosis, margine truncatis, æstivatione valvatis: discus ibidem connatus, stellæformis, 5lobus, carnosus, glaber, coloratus, nectariferus? è basibus dilatatis filamentorum alternorum constitutus, ejusdemque lobis a calyce parùm elevatis, subrotundis, emarginatis! Petala 5, calycinis laciniis alterna, spathulata, unguic ulata. Stamina 10, duplici ordine disposita; 5 exteriora loborum disci emarginaturis, et hinc medio calycinarum laciniarum inserta; cætera fauci calycis tomentosa inserta, petalisque opposita : filamenta subulata, glabra: antheræ introrsæ, biloculares, peltato modo insertæ loculis apice confluentibus, rimâ longitudinali dehiscentibus. Ovaria 5, tomentosa, in unum 5-angulum quasi connata. Styli '5, distincti, compressi, glabriusculi, terminales, subinde maturescenti fructu unilaterales. Stigmata totidem, unilateralia, recurvato-patentia, minutissimè papillosa. Fructus: folliculi 5, connati, patentes, stylo unilaterali, persistenti instructi, uniloculares, polyspermi, suturâ filiformi utrinque dehiscentes: valvis ventricosis, crustaceis, intùs politis. Semina basi interiori loculorum inserta, adscendentia, apice alâ obliquâ membranaceâ punctatissimâ instructa: umbilico basilari: testá simplici, crustaceâ. Cætera ut in ordine. Arbores (Chil. et Bras.) sempervirentes. Folia alterna, petiolata, indivisa. Stipulæ 2, petiolares, caduca. Flores corymbosi. 1. Q. saponaria, foliis ovalibus plerumque dentatis. Quillaja saponaria, Mol. Hist. Nat. Chil. p. 182. ed. 2. 298.—Poir. Dict. 6. p. 33. Q. smegmadermos, Decand. Prod. 2. p. 547. Smegmadermos emarginatus, Ruiz et Pavon Syst. Veg. Fl. Peruv. et Smegmaria emarginata, Willd. Sp. Pl. 4. p. 1123.—Spreng. Syst. Veg. 2. Hab. in Chili sylvis copiosè in Rere et Puchacay provinciis.-Ruiz et Arbor procera (60-pedalis), frondosissima, sempervirens. Ramuli teretes, pubescentes. Folia alterna, petiolata, ovalia v. rarò oblonga, obtusa, sæpiùsque emarginata, margine plerumque dentata, sæpè tamen inte gerrima, coriacea; juniora leviter velutina; adulta utrinque glabra, viridia, lucidula, costâ subtùs prominulâ venisque angulo acuto obliquè transversis vix conspicuis, sesquipollicaria, pollicem lata. Petioli brevissimi, vix lineam longi. Stipule 2, parvæ, lanceolatæ, acutæ, membranaceæ, canaliculatæ, puberulæ, fuscescentes, caduca, petiolo cuique adnatæ vix longiores. Flores albi? plerumque terminales, subsolitarii, aut plures (3 v. 5) corymbosi. Pedunculi semunciales cum pedicellis brevissimis angulati, densè velutini, incani. Bracteole oblongæ, obtusæ, canaliculatæ, coriacea, tomentosa, deciduæ. Petala vix calyce longiora. OBS. 1. Cortice saponis loco ad vestimenta lanea mundificanda incolæ utuntur; et ex eodem contuso globulos magnos conficiunt et dimidio regali singulos venditant.-Ruiz et Pavon, 1. c. OBS. 2. Folia exsiccata sæpè colorem æruginosum usurpant. Testa seminis embryone increscente sæpè basi disrupta ! Planta a Molinâ pessimè descripta. 2. Q. lancifolia, foliis lanceolatis acutis. Hab. in Brasiliâ.-Sello. h. (V. s. sp. in Herb. Lamb.) Arbor facie peculiari ferè ad Persoonias quibusdam accidens. Ramuli te. retes, pube tenerrimâ vestiti. Folia alterna, petiolata, lanceolata, acuta, cartilaginea, utrinque glaberrima, costâ venisque obliquè rectis, prominulis, ramosis instructa, suprà viridia, lucida, subtùs pallidiora, opaca, basi attenuata, 2-3-pollicaria, semunciam vix ultra lata: margine obtuso, calloso, parùm incrassato, integerrimo, v. rarò nonnullis prominentiis (dentibus obsoletis) ornato. Petioli 2-3 lineas longi, suprà planiusculi. Stipule 2, parvæ, oblongæ, cartilagineæ, fuscescentes, caducæ. Flores 5 v. 7, corymbosi, terminales et axillares, sed ple rumque axillares. Pedunculi vix semipollicares, angulati, calycesque dense velutini, incani. Ovaria 5, densè tomentosa, coalita. Petala calyce longiora. Disci lobi crassiores, magisque elevati. Stamina longiora. Filamentà alterna parùm infra loborum disci apices inserta. Styli pubescentes recurvato-patentes, paullò crassiores. Cætera omnino ut in genere. KAGENECKIA, Ruiz et Pavon. Calyx crateriformis, extùs 10-costatus, fructu maturescenti auctus! persistens: limbo 5-fido, intùs annulo parùm elevato, vix membranaceo, ovaria circumcingenti instructo: lobis ovatis, acuminatis v. obtusis, recurvatopatulis. Petala nulla? Stamina definitè numerosa (15); quorum 5 lobis calycinis alterna; cætera per paria lobis iisdem opposita: filamenta subulata compressa, persistentia, basi dilatata, et in annulum conferruminata, atque subinde totum indumentum faucis et cavitatis calycis constituunt : antheræ cordato-oblongæ, introrsæ loculis basi solutis, divergentibus, ad apicem usque distinctis, nec confluentibus, longitudinaliter dehiscentibus. Ovaria in circulum digesta, unilocularia: ovulis pluribus, erectis. Styli compressi, glabri, terminales. Stigma complicatum, ferè ut in Delphinio, disco cucullato, demùm marginibus reflexis convexo, densè papilloso. Capsule 5, folliculares, omninò ut in Pæoniâ, densè sericeo-tomentosæ, exteriùs maximè productæ, et subinde stylus quasi unilateralis, polysperma. Semina apice membranaceo-alata, samaroidea, angulo interiori locuri inserta, imbricata, declinato-horizontalia: umbilico basilari: testa simplex, ob interiorem exteriori intimè adhærentem, membranacea : albumen nullum. Embryo erectus, lutescens: cotyledones subrotundo-cordatæ, foliaceæ, costâ prominenti subcarinatæ, contrariè convolutæ ! inæquilateræ, sesquilineam latæ ; lobo altero minore, accumbenti: radicula teres, crassa, obtusissima, cotyledonibus triplò brevior, centripeta. Plumula conspicua. Arbores (Amer. Austr.) Folia alterna, simplicia, impunctata, serrulata: denticulis glandulosis. Stipulæ minima, glandulæformes, caduca. Flores terminales, polygami. OBS. Dubito anne flores verè omninò apetali, atque in eadem v. diversâ arbore sexu distincti. 1. K. oblonga, foliis oblongis obtusis coriaceis: denticulorum glandulis deciduis, floribus solitariis. Kageneckia oblonga, Ruiz et Pavon Syst. Veg. Fl. Peruv. et Chil. 1. p. 289. Lydæa Lyday, Mol. Hist. Nat. Chil. ed. 2. 300. Hab. in Chili montibus ad Conceptionis urbem.-Ruiz et Pavon. h. Arbor 6-orgyalis, sempervirens. Folia petiolata, oblonga, v. rariùs obo. |