G R I 



[ us 1 



GYP 



and may be observed lying on the sea- 

 shore in considerable numbers, after a 

 recent fall of the cliff. Upon comparing 

 the sandstone of Stonehenge with that of 

 Sussex, no perceptible difference can be 

 detected. 



GRI'SEOUS. (from yriser, Fr.) A mix- 

 ture of black and white. 



GRIT. The provincial term for a coarse 

 siliceous sandstone. Some of the strata 

 of this description have been worked for 

 mill-stones, from which circumstance 

 they have been called mill-stone grit. 

 The mill-stone grit is an important depo- 

 sit in the north of England, from the 

 Coquet to the Tyne, and on the hills be- 

 tween the dales of Durham and York, 

 from the Tyne to the Kibble. 



GROSSULA'RE. The asparagus-green va- 

 riety of dodecahedral garnet. It is found 

 in Siberia. Its constituents are, silica 

 40-50, alumina 20'10, lime 33-80, oxide 

 of iron 5'00, oxide of managanese 0'50. 



GRYPH^'A. (from gryps, Lat. a griffin.) 

 A fossil inequivalved bivalve ; the lower 

 valve concave, terminated by a beak, and 

 curving upwards and inwards ; the upper 

 valve much smaller, like an operculum ; 

 the hinge toothless, the pit oblong and 

 arched : one impression in each valve. 

 Fossil shells of this genus are found in 

 considerable numbers in different parts 

 of England. From the curved beak of 

 the shell, Linnaeus placed it among the 

 anomise ; but Lamarck placed it under a 

 distinct genus. He notices nine dif- 

 ferent species. Parkinson observes, " on 

 viewing the different specimens of ostra- 

 cites and gryphites, I cannot help doubt- 

 ing as to the propriety of the formation 

 of a distinct genus for this shell. T find 

 specimens in which the beak and the 

 body of the valve possess various degrees 

 of curvature, from the complete curve of 

 the gryphites to the slight turn of the 

 edible oyster. The recent gryphsea is 

 found at a shallow depth, in estuaries, on 

 gravel and sand. 



GRYPHI'TE. (gryphites, Lat.) Belonging 

 to the genus gryphsea. This deeply- 

 incurved bivalve is so abundant in some 

 of the beds of lias in France, as to have 

 occasioned them to be called Galcaire a 

 gryphites. These shells are known in 

 this country by the provincial term of 

 " miller's thumbs." 



GYMNOSPE'RMIA. (from yv^ivog, nudus, 

 naked, and (TTrlp^a, semen, seed.) The 

 first order in the fourteenth class, Didy- 

 namia, in Linnseus's artificial system ; 

 having four naked seeds in the bottom of 

 the calyx, with the exception of one 

 genus, Phryma, which is monosper- 

 mous. 



GYMNOSPE'RMOUS. Having naked seeds 



in the bottom of the calyx ; belonging to 

 the order Gymnospermia. 



GYNA'NDRIA. (from yvvri, a woman, and 

 avrjp, Gr. a man.) The name of the 20th 

 class in Linnseus's sexual system, con- 

 sisting of plants with hermaphrodite 

 flowers, having the stamens growing upon 

 the style, or having the stamina united 

 with, or growing out of the pistil, and 

 either proceeding from the germen or the 

 style. The orders of this class are taken 

 from the number of the pistils, but bo- 

 tanists are not agreed as to the admission 

 of some of them into the class. 



GYNA'NDRIAN. Belonging to the class 

 Gynandria. 



GYNA'NDROUS. A term applied to a par- 

 ticular class of plants, in which the sta- 

 mens and pistils are united. The orders 

 of this class depend on the number of the 

 anthers. 



GY'PSEOUS. (gypseux, Fr.) Resembling 

 gypsum ; containing gypsum ; of the na- 

 ture of gypsum. 



GY'PSUM. ( yttyoff, Gr. gypsum, Lat. gypse, 

 Fr. gesso, It.) The chaux sulfatee of 

 Brongniart and Haiiy. Sulphate of lime ; 

 it is composed of sulphuric acid 46'0, 

 lime 33'0, water 21 . It possesses double 

 refraction. There is one variety known 

 by the name of anhydrite, or anhydrous 

 gypsum, which contains no water. Sul- 

 phate of lime is an abundant mineral 

 salt, presenting itself under various forms, 

 crystallized or otherwise. From gypsum 

 is obtained plaster of Paris, the gypsum 

 being burnt in a kiln, and the water 

 thereby driven off. The varieties of 

 gypsum are numerous ; the crystallized 

 transparent varieties are known as se- 

 lenite ; the fibrous and earthy as gypsum ; 

 and the granular and massive as alabas- 

 ter. The salt mines of this country 

 afford examples of nearly all the varieties. 

 The white powder obtained by exposing 

 gypsum to a strong heat has obtained the 

 name of plaster of Paris, from the ex- 

 treme abundance of this mineral in the 

 neighbourhood of that capital. Its infe- 

 rior hardness, together with its chemical 

 characters, will serve to distinguish it 

 from the carbonate, fluate, and phos- 

 phate of lime. " The gypsum formation 

 consists of alternating beds of gypsum 

 and argillaceous and calcareous marl, 

 which are regularly arranged, and pre- 

 serve the same order of succession where- 

 ever they have been examined. The 

 gypsum forms three distinct masses. The 

 lowest consists of thin strata of gypsum 

 containing crystals of selenite, which al- 

 ternate with strata of solid calcareous 

 marl, and with argillaceous shale. The 

 middle is like the lowest mass, except 

 that the strata of gypsum are thicker, 

 Q 



