C H A 



[83] 



C H A 



land. The third range, leaving 

 Wilts and Berks, enters Hants, 

 and to the south passes round 

 Petersfield, then, stretching to the 

 east, forms a barrier against the 

 sea along the coast from Chiehester, 

 constituting the South Downs, 

 ranging from Mapledurham to 

 Beachy-head. For a description of 

 the organic remains of the chalk 

 formation, the reader is referred to 

 the article Cretaceous group. 

 CHALK MARL. (Craie Tufau, Fr. 

 Kreide mergel, Germ.) The beds 

 of chalk marl, says Mr. Conybeare, 

 which occur immediately beneath 

 the chalk, graduate into the lowest 

 strata of that subtance, in such a 

 manner that very often no distinct 

 line of separation can be traced. 

 On the other hand, the lowest beds 

 of the chalk marl often pass into 

 those of the green sand, and it is 

 sometimes difficult to catch any 

 precise characters for a formation 

 which is thus rather intermediate 

 between two others, than possessed 

 of independent features. The com- 

 position of these beds consist appar- 

 ently of three ingredients, intimately 

 blended, but in various proportions; 

 cretaceous matter ; argillaceous 

 matter; and sand. In the upper 

 beds, the cretaceous matter is the 

 most abundant ; and these commonly 

 have the appearance of chalky beds, 

 but distinguishable from the true 

 chalk by a mottled or greyish 

 character, by a more laminated 

 texture, and by falling to pieces 

 when dried, after having been 

 wetted. When the argillaceous 

 matter greatly prevails, a tenacious 

 bluish-grey marl is the result. 

 When the sand prevails, a fine- 

 grained grey-coloured sandstone, 

 having a loose texture, is produced; 

 and this last is found graduating 

 into the green sand. The chalk 

 marls attain a thickness, in some 

 situations, of from 300 to 500 feet. 

 The inclination of the strata is 



conformable to that of the super- 

 jacent chalk, being usually nearly 

 horizontal, but where, as in some 

 situations, the chalk has been tilted 

 up, as in the Isles of Wight and 

 Purbeck, there also will the chalk 

 marl be found in conformable posi- 

 tion. The chalk marl has been 

 called by some authors grey marl. 

 For further particulars see Grey marl. 



CHA'LICO-THEBIUM. An extinct animal, 

 belonging to the order of Mammalia, 

 allied to the tapir, and referrible to 

 the miocene period. 



CHAMA. (Animal a chiton.) A genus 

 of inequivalved adhering bivalves, 

 with unequal incurvated beaks. 

 It is placed both by De Blain- 

 ville and Lamarck in the family 

 ChamaceaB, together with Diceras, 

 Etheria, &c. Bruguiere limits this 

 genus to those shells possessing a 

 single hinge-tooth only. Many 

 species have been found fossil, 

 more particularly in the neighbour- 

 hood of Paris. The shells of this 

 genus are inhabitants of the ocean, 

 and live in deep water. Twenty- 

 five species have been described; 

 one only of these has been dis- 

 covered in our seas, namely, the 

 Chama Cor. 



CHAMA'CEJE. A family of bivalves 

 placed by Lamarck in the order 

 Dimyaria, and by De Blainville in 

 the order Lamelli-branchiata. It 

 comprises the genera chama, diceras, 

 etheria, isocardium, trigonia, &c. 



CHA'MA GIGAS. (The Tridacna of 

 Lamarck.) A species of chama 

 inhabiting the Indian ocean ; it is 

 the largest and heaviest shell yet 

 discovered, being sometimes of the 

 enormous weight of 530 pounds, 

 and its occupant so large as to 

 furnish one hundred and twenty 

 men with a meal ; it is said to be 

 very palatable. Fossil shells of 

 the chama gigas are collected by 

 the inhabitants of the East Indian 

 archipelago, for the purpose of being 

 formed into armlets and bracelets. 



