C H A M A C H A M O R C H I S. 



occupies the interior area of the great central basin 

 of Europe. This concavity is bounded on the north 

 by the primitive mountain districts of Russian Fin- 

 land, Sweden, Norway, and Scotland ; on the west 

 bv the transition and primitive chains of Cumberland, 

 Wales, Devonshire, and Britany ; on the south by 

 the primitive mountains branching from the Cevennes 

 in the centre of France, the Alps, with the various 

 grand groups of Germany, as the Black Forest, the 

 Rhingau and the Vosges, the Bohemian, Thuringian, 

 Saxon, Silesian, and Carpathian mountains ; on the 

 east by the Ural chain and its branches. The chalk 

 does not rest on the mountains themselves, but within 

 the area which they circumscribe at a certain distance 

 from them, an interior area may be traced, over which 

 the substratum of chalk is believed to extend. 



Cuvier and Bronerniart represent the chalk deposit 

 as forming a sterile soil, and adduce Champagne as a 

 proof of its being in some cases uninhabitable. In 

 our own country the population of the chalk district 

 is certainly less dense than that of many other parts, 

 but it is usually habitable, and to a certain extent 

 productive. Indeed we may say that the chalk 

 valleys are often in this country extremely fertile, of 

 which the Kent and Surrey hop grounds, and the 

 downs for pasturing sheep, afford examples. Beech 

 is the tree best fitted for a chalky soil. The Chiltern 

 Hills, in Oxfordshire, were anciently covered with 

 woods and thickets of beech, which afforded harbour 

 to banditti. The lower beds of the chalk formation 

 are, with few exceptions, filled with water, which 

 percolating from above is arrested by the subsoil of 

 blue clay. Thus are formed the springs and rivulets 

 which issue near the foot of almost every chalk hill. 



It is remarkable that America, both South and 

 North, seems to be destitute of chalk, Mr. Maclure 

 asserting positively that it does not exist on that 

 continent. Chalk is well known to have an earthy 

 dull fracture, but it occasionally concretes into a hard 

 limestone. This compact chalk has been used in 

 building. As tins formation is composed throughout 

 of a series of homogeneous beds of a tender earthy 

 limestone, it does not admit of stratiform sub- 

 divisions. 



But the numerous beds of nodular flints, which lie 

 alternately distributed through the greater part of its 

 mass, form one of its most curious and essential fea- 

 tures. They are constantly present in all the upper 

 portions of the formation, but are frequently absent 

 in the lower ; affording a criterion by which the two 

 may be distinguished. Hence the meaning of the 

 terms upper and lower chalk. 



The uses of this mineral are various. The more 

 compact kinds are employed as building-stones, when 

 they are used either in a rough state, or are sawn into 

 blocks of the requisite size and shape ; it is burnt into 

 quicklime, and used for mortar in different countries ; 

 it is also employed in great quantities in the polishing 

 of glass and metals, and whitening the roofs of rooms 

 in the state of whitening ; in constructing moulds to 

 cast metal in ; by carpenters and other artisans to 

 mark with. When perfectly purified, and mixed with 

 vegetable colours, it forms a kind of pastil colour ; 

 thus, with litmus, turmeric, saffron, and sap-green, it 

 forms durable colours. The Vienna white known to 

 artists is perfectly purified chalk. It is also used by 

 starch-makers and chemists to dry precipitates on, 

 for which it is peculiarly qualified, on account of the 

 remarkable facility with which it absorbs water. 



CHAM A. Lamarck, in constituting this gcuus, 

 has separated from the Linnaean arrangement al. 1 

 such shells as have only a thick oblique transverse 

 tooth, resembling a lengthened callosity, in general 

 crenulated or grooved, fitting into a corresponding 

 cavity in the lower valve. The shell is inequivalve, 

 irregular, heavy, rough, scaly, or spinous, having the 

 faculty of affixing itself to other bodies, or to each 

 other in groups, by means of its lower valves. The 

 apices are unequal and recurved ; valves with two 

 distinct distant lateral muscular impressions; ligament 

 external and inserted. The characters of these shells, 

 in some respects, ally them to the genus Die-eras, and 

 in others to the genus Etkerut. They are, most of 

 them, elegant shells, some with delicate waved or 

 foliaceous valves, some with spines, and pleasingly 

 coloured with yellow, pink, and brown. The animal 

 possesses a suborbicular body, terminated on the 

 upper side with a sort of hook-mantle slightly opened, 

 the foot terminated at its extremity by a portion 

 much narrower than the base ; the superior lobes of 

 the branchia very short. The following subdivision 

 of this genus, though not exactly in unison with those 

 of Lamarck, appear to us natural and well defined : 

 1st, The species that are irregular, inequivalve, with- 

 out lunulae, adhering by the left and largest valve-, 

 the two summits turning more or less in a spiral form, 

 the left summit more prolonged than the right, as in 

 the Chama Lazarus, and in the same division, those 

 whose summits are prolonged nearly equally, as in the 

 C. gryptundes. 2nd, The species subequivalve, sub- 

 regular, with a distinct lunula, the summits but 

 slightly spiral, adhering by either valve, as in the 

 C. arcinella. 3rd, The species which are subregular, 

 half-heart shaped, very inequivalved, the right valve 

 much excavated, the left valve operculated, one conical 

 cardinal tooth, smooth on one side, and fitting into a 

 deep groove on the other valve ; ligament as if double, 

 the internal portion much thicker than the external, 

 the muscular impression anterior and very long, as in 

 the Chama hemicardium. 



This genus is extremely difficult to characterise by 

 any system of teeth or hinge, for each species presents 

 a particular modification, nevertheless, the last division 

 named is so peculiarly different from the others, that 

 without any reference to the animal, it might well 

 form a distinct genus. 



These shells are found in all the seas but those of 

 the north ; in the southern seas they are more numer- 

 ous than elsewhere. Eight or ten species are known 

 in a fossil state. They are classed in the third 

 class, Acephalopftora ; third order, Lamcllibranchiata ; 

 seventh family, Camacea. 



CHAMvEROPS (Linnaeus). A genus of palms, 

 commonly called the fan-palm. Linntean class and 

 order Polygamia Diaecia; natural order Palnue. (ie- 

 neric character : flowers polygamous ; spatha double, 

 leathery, interior side bursting obliquely ; florest 

 sitting and bractiate; calyx three-cleft; corolla of 

 three petals ; filaments dilated at the base, and con- 

 nected; stigma three, awl-shaped ; berries three, one- 

 seeded. This palm thrives best in sandv loam, and 

 requires moist heat. It is found in the south of 

 Europe, and all warm countries. 



CHAMORCHIS (Richard). A single plant 

 forming a new genus, formerly called Opkrys Alpina 

 by Linnaeus. Like other orchises it has tuberous 

 roots, which are liable to be lost if not planted in 

 turf, and kept in a station like their natural one. 



