GLOSSARY. 



75 



substance, of which there are springs in many countries, parti- 

 cularly in volcanic districts. 



NENUPHAR. A yellow water-lily. 



NEW RED SANDSTONE. A series of sandy, argillaceous, and often 

 calcareous strata, the predominant colour of which is brick-red, 

 but containing portions which are of a greenish grey. These 

 occur often in spots and stripes, so that the series has some- 

 times been called the variegated sandstone. The European 

 formation so called lies in a geological position immediately 

 above the coal-measures. See Table II. K, p. 392. 



NODULE. A rounded irregular-shaped lump or mass. Etym., dimi- 

 nutive of nodus, knot. 



NORMAL GROUPS. Groups of certain rocks taken as a rule or stand- 

 ard. Etym. norma, rule or pattern. 



NUCLEUS. A solid central piece, around which other matter is col- 

 lected. The word is Latin for kernel. 



NUMMUHTES. An extinct genus of the Order of Molluscous animals, 

 called Cephalopoda, of a thin lenticular shape, internally divided 

 into small chambers. Etym., nummus, Latin for money, and 

 Ai0og, lithos, stone, from its resemblance to a coin. 



OBSIDIAN. A volcanic product, or species of lava, very like com- 

 mon green bottle-glass, which is almost black in large masses, 

 but semi-transparent in thin fragments. Pumice-stone is 

 obsidian in a frothy state ; produced most probably by water 

 that was contained in or had access to the melted stone, 

 and converted into steam. There are very often portions in 

 a mass of solid obsidian, which are partially converted into 

 pumice. 



OGYGIAN DELUGE. A general inundation of fabulous history, which 

 is supposed to have taken place in the reign of Ogyges in 

 Attica, whose death is fixed in Blair's Chronological Tables in 

 the year 1764 before Christ. 



OLD RED SANDSTONE. A stratified rock belonging to the Carbon- 

 iferous group. See Table L, p. 393. 



OLIVINE. An olive-coloured, semi-transparent, simple mineral, very 

 often occurring in the forms of grains and of crystals in basalt 

 and lava. 



OOLITE, Oolitic. A limestone, forming a characteristic feature of a 

 group of the secondary strata. See Table II. H, p. 391. It 

 is so named, because it is composed of rounded particles, like the 

 roe or eggs of a fish. Etym. wov, oon, egg, and Xt0o, lithos, 

 stone. 



