GAL 



C 102 ] 



GAS 



the shell rises in a vaulted, helmet-like, 

 form. 



GALEO'LA. A genus of echinites possess- 

 ing the same characters as the galea, but 

 differing in size. This circumstance in- 

 duced Klein to divide them into two 

 genera, but Leske deeming a mere dif- 

 ference of size as insufficient to affect the 

 genus, included them both under the 

 genus echinocorys. Parkinson. 



GA'LEATED. (galealus, Lat.) Helmet- 

 shaped ; covered as with a helmet. In 

 botany, plants beai'ing flowers of a helmet 

 shape, as the monk's-hood. 



GALE'NA. (galena, Lat.) A shining me- 

 tallic ore composed of sulphur and lead ; 

 sulphuret of lead ; lead-glance. Its colour 

 is bluish-grey, resembling lead. Occurs 

 regularly crystallized, frequently in cubes 

 and cubo-octahedrons. Before the blow- 

 pipe it decrepitates and melts, emitting a 

 sulphureous smell. It is found in every 

 lead-mine. There are two varieties, 

 common galena and compact galena. 



GALLINA'CE^E. Gallinee of Linngeus. The 

 fourth order of the second class, Aves. 

 So called from their affinity with the do- 

 mestic cock. 



GALLINA'CEOUS. (yallinaceus, Lat.) Be- 

 longing to the order Gallinaceae. 



GALT. } A provincial name for a stiff marl, 



GAULT. $ varying in colour from a light 

 grey to a dark blue. The upper and 

 lower beds of the green-sand are in many 

 places separated by the gait ; it has been 

 also called Folkstone Marl. The gait 

 abounds in fossil remains, remarkable for 

 their beauty, the pearly covering of the 

 shells being in many instances preserved. 

 The gault is a member of the cretaceous 

 group, passing, in its lower parts, into 

 calcareous marl. The fossils hitherto 

 found in the gait belong to forty-three 

 species, among which are several species 

 of ammonites and hamites ; nautili and 

 belemnites ; nucula? and inocerami ; cary- 

 ophillea, &c. The gait rarely exceeds 

 100 feet in thickness ; although in some 

 parts of Sussex it is not less than 250. 

 It is a soil that must rank, says Mr. 

 Young, among the finest in this or any 

 other country, being pure clay and calca- 

 reous earth. 



GAMOPE'TALOUS. Another term for mo- 

 nopetalous. Having the petals united by 

 their edges ; a corolla, the petals of which 

 are all united by their edges. 



GAMOSE'PALOUS. In botany, a term used 

 for a calyx when the sepals of which it is 

 composed are all united. 



GA'NOID. Belonging to the order Ganoi- 

 dian. 



GANOI'DIANS. (from ydvog, Gr. splendour, 

 from the brightness of their enamel.) 

 The second order of fishes according to 



the arrangement of M. Agassiz. The 

 families of this order are characterized by 

 angular scales, composed of horny or 

 bony plates, covered with a thick plate of 

 enamel. The bony pike and sturgeons 

 are of this order. It contains more than 

 sixty genera, of which fifty are extinct. 

 Prof. Bucldand. 



GANOI'DIAN. Belonging to the order Ga- 

 noidia. The ganoidian order of fishes 

 with the placoidean prevailed, exclusively, 

 in all formations till the termination of 

 the oolitic series, when they ceased sud- 

 denly and were replaced by genera of new 

 orders, the Ctenoidean and Cycloidean, 

 then for the first time introduced. Ib. 



GAP. In conchology, an opening, in mul- 

 tivalves and bivalves, when the valves are 

 shut, as in the pholades, myse, &c. 



GA'RNET. (grenat, sorte de pierre preci- 

 euse, d'un rouge f once, comme le gros vin, 

 Fr. granato, It. pietra preziosa. ) There 

 are eleven species of garnet, all of them 

 crystals. The precious garnet is found in 

 dodecahedrons, in mica-slate, amongst 

 the oldest, or primary, rocks, in many 

 parts of the world. It is of a beautiful- 

 red colour, sometimes with shades of yel- 

 low or blue. Those from the kingdom of 

 Pegu are most esteemed, and it is sup- 

 posed that this was the carbuncle of the 

 ancients. It is harder than quartz, and 

 consists of nearly equal parts of silex, 

 alumine, and oxide of iron, with traces of 

 manganese. Common garnets are more 

 opaque, of a duller colour, and less hard 

 than the precious garnet, though harder 

 than quartz. They are abundant in simi- 

 lar localities in all countries, sometimes 

 constituting nearly the whole mass of a 

 rock. 



GAS. The name given to all permanently 

 elastic, or aeriform, fluids, except the 

 atmosphere. The term was first used by 

 Van Helmont, who appears to have in- 

 tended to denote by it every thing which 

 is driven off from bodies in the state of 

 vapour by heat. 



GA'SEOUS. (from gas.) In the form 

 of gas. 



GASTE'ROPOD. Belonging to the order 

 Gasteropoda. 



GASTERO'PODA. (from yaarrip, the belly, 

 and TTOVQ, the foot, Gr. ) The third 

 class of Mollusca ; they have the head 

 free, they crawl upon the belly, or upon 

 a fleshy disk, situated under the belly, 

 which serves them as feet. They are 

 univalvular or multivalvular, but in no 

 case bivalvular. The back is furnished 

 with a mantle which is more or less ex- 

 tended, takes various forms, and in the 

 greater number of genera, produces a 

 shell. The tentacula are very small, si- 

 tuated above the mouth, and do not sur- 



