GEE 



[206 ] 



G R E 



GEE':N"ATITE. Prismatoidal garnet. 

 See Granitite and Staurotide. 



GEES DE VOSGES. " A very extensive 

 deposit," says De la Beche, " occurs 

 in the Yosges, and has thence 

 obtained its name. A difference 

 of opinion seems to exist between 

 M. Elie de Beaumont and M. Voltz 

 respecting the exact member of the 

 red sandstone series to which this 

 rock should be referred ; the former 

 considering it the equivalent of the 

 Bothe Todte Liegende, which occurs 

 beneath the zechstein ; the latter, 

 that it is the lower portion of the 

 red or variegated sandstone, which 

 rests on the zechstein. It is essen- 

 tially composed of amorphous grains 

 of quartz, commonly covered by a 

 thin coating of red peroxide of iron; 

 among which are discovered others 

 which appear to be fragments of 

 felspar crystals. The rock con- 

 tains quartz pebbles, sometimes 

 so abundantly as to present a 

 conglomerate with an arenaceous 

 cement. It is also often marked 

 by cross and diagonal laminae. 



GEES BIGAEEE. (from two French 

 words, signifying a stone formed 

 of grains variously coloured.) The 

 name given by French geologists 

 to that member of the red sandstone 

 group known as the new red sand- 

 stone ; the hunter sandtein of the 

 Germans. 



GEEY MAEL. (The Craie Tufeau of 

 French geologists.) One of the 

 members of the chalk formation, 

 placed above the firestone or upper 

 green sand and below the chalk 

 without flints. Where, as is 

 sometimes the case, the firestone is 

 absent, the grey marl is found 

 reposing immediately upon the 

 gault. In Sussex, says Dr. Man- 

 tell, this deposit constitutes the 

 foundation of the chalk hills, its 

 outcrop forming a fillet or zone 

 round their base, and connecting 

 the detached parts of the range 

 with each other. 



The marl is commonly soft and 

 pliable, but indurated blocks occur 

 which possess the hardness of lime- 

 stone. It is of a light grey colour, 

 inclining to brown, and frequently 

 possesses a ferruginous tinge, de- 

 rived from oxide of iron. It con- 

 sists principally of carbonate of 

 lime and alumine, with an inter- 

 mixture of silica, a very small 

 proportion of iron, and perhaps of 

 oxide of manganese. 



The mineralogical productions, 

 says the same talented author, in 

 his Geology of the South-east of 

 England, of the grey marl are few, 

 and offer but little variety : they 

 consist of various modifications of 

 sulphuret of iron, and crystallized 

 carbonate of lime. In organic 

 remains, the grey marl is very 

 rich, and these differ both in their 

 nature, and in the mode of their 

 preservation, from those of the 

 lower chalk above, and of the gault 

 beneath. Ammonites, hamites, 

 nautilites, turrilites, scaphites, 

 pectenites, madreporites, inocerami, 

 rostellarise, and auriculae, together 

 with the teeth and vertebrae of 

 sharks, are found in different parts 

 of this deposit. No parts of England 

 are supposed to be so rich in the 

 various species of turrilites as the 

 marl pits in the neighbourhood of 

 Lewes. A specimen of turrilites 

 tuberculata nearly two feet long, 

 the only instance in which traces 

 of a siphunculus are visible, was 

 discovered in the grey marl at 

 Middleham, near Lewes. 



GEE'YSTONE. A rock of greyish or 

 greenish colour, composed of felspar 



" and augite, the former being more 

 than 75 per cent, of the whole. 



GREY-WEATHEES. The name given to 

 large boulders of siliceous sandstone. 

 There is a singular assemblage of 

 these erratic blocks in a field on 

 the borders of Wiltshire, not far 

 from Marlborough. The immense 

 blocks forming, as is supposed, the 



