U M 



[319] 



B L 



termed Lentes lapidese, Lapides 

 cumini, circulares, numismales, &c. 



Nummulites vary in size from 

 less than an eighth of an inch, or 

 even microscopic minuteness, to an 

 inch and a half in diameter. Their 

 surface is, in some, nearly smooth, 

 in others rough and scabrous, with 

 numerous small projecting knobs, 

 or undulating lines. Their colour 

 varies from nearly white to brown 

 and red, and sometimes nearly blue. 

 The number of spiral turns seems 

 to depend on the age and size of 

 the animal; in those of a quarter 

 of an inch in diameter, being three 

 or four, while in those of the largest 

 size the number of whorls is fre- 

 quently upwards of twenty. 



Nummulites occupy an important 

 place in the history of fossil shells, 

 on account of the prodigious extent 

 to which they are accumulated in 

 the later members of the secondary, 

 and in many of the tertiary strata. 

 They are often piled on each other 

 nearly in as close contact as the 

 grains in a heap of corn. Entire 

 calcareous hills are, in some in- 

 stances, composed of fossil nummu- 

 lites. 



NTTMMTJLI'TIC. Containing nummu- 

 lites; composed of nummulites. 

 The nummulitic limestone of the 

 Alps, a formation which extends 

 through all the countries surround- 

 ing the Mediterranean, and thence 

 through Lower Asia into India, and 

 which is many thousands of feet in 

 some places, has been shown by 

 Sir B. Murchison to be clearly 



referrible to the eocene period. 

 Jukes. 



NUTA'TION. (from nutatio, a nodding, 

 Lat. nutation, Fr.) A tremulous or 

 vibratory motion of the earth's axis, 

 by which its inclination to the plane 

 of the ecliptic is continually vary- 

 ing, being, in its annual revolution, 

 twice inclined to the ecliptic, and 

 as often returning to its former 

 position. Both the celestial lati- 

 tudes and longitudes are altered to 

 a small degree by nutation. In 

 consequence of this real motion 

 in the earth's axis, the pole-star, 

 forming part of the constellation of 

 the Little Bear, which was formerly 

 12 from the celestial pole, is now 

 within 1 24' of it, and will con- 

 tinue to approach it till it is within 

 J, after which it will retreat from 

 the pole for ages ; and 12,934 years 

 hence, the star a Lyrae will come 

 within 5 of the celestial pole, and 

 become the polar star of the north- 

 ern hemisphere. 



NUT-GALL. An excrescence which 

 grows on some species of oaks. 

 These excrescences are produced 

 by the Cynip quercus folii, of Lin- 

 naeus, a small insect which deposits 

 its egg in the tender shoots of the 

 quercus infectoria, a species of oak 

 abundant in Asia Minor. When 

 the maggot is hatched, it produces 

 a morbid excrescence of the sur- 

 rounding parts, and it ultimately 

 eats its way out of the nidus thus 

 formed, and makes its escape. The 

 best galls are imported from Smyrna 

 and Aleppo. 







OB'CONTCAL. Of the shape of a re- 

 versed cone. 



OBCO'BDATE. In botany, an epithet 

 for an inversely heart-shaped leaf, 

 petal, or legume. 



O'BLATE. (ollatus, Lat.) Flattened 

 or depressed at the poles ; generally 

 applied to spherical bodies, flattened 

 at the poles; of the shape of an 

 orange. 



