ALL 



t 



ALT 



of calcareous tufa. " These forma- 

 tions appear to have proceeded 

 uninterruptedly, as at present, from 

 the period when our continents 

 assumed their present form." Rev. 

 J. Conyleare. 



ALLUVIAL EPOCH. Some writers have 

 attempted, says Sir C. Lyell, to 

 introduce into their classification of 

 geological periods an alluvial epoch, 

 as if the transformation of loose 

 matter from one part of the surface 

 of the land to another had heen 

 the work of one particular period. 

 With equal propriety might they 

 have endeavoured to institute a 

 volcanic period, or a period of 

 marine or fresh-water deposition, 

 for alluvial formations must have 

 originated in every age since the 

 surface of the earth was first 

 divided into land and sea. 

 ALLU'VION. | (alluvia, ~L&i. alluvion,!??. 

 ALLU'VITJM. ) alluvione, It.) Earth, 

 sand, gravel, stones, or other trans- 

 ported matter which has been 

 washed away and deposited by 

 water upon land not permanently 

 submerged beneath the waters of 

 lakes or seas. Lyell. 



Alluvium has been divided into 

 modern and ancient. The modern, 

 characterized by the remains of 

 man, and contemporaneous animals 

 and plants; the ancient, by an 

 immense proportion of large mam- 

 malia and carnivora, both of extinct 

 and recent genera and species. The 

 term alluvium has been assigned to 

 the partial debris occasioned by 

 causes still in operation; such as 

 the wear produced by the present 

 rivers, the more violent action of 

 torrents, &c. The Hon. W. Fox 

 Strangways dates the commence- 

 ment of the alluvium from the 

 period of the retreat of the last 

 waters that have covered the earth, 

 and includes under it 



1. Drift sand, marine, or inland. 



2. Marsh land, composed of mud 

 deposited by riyer*. 



3. Peat. 



4. Calcareous tufa. 



To these may be added beds of 

 gravel, produced locally by torrents 

 and rapid rivers. All these for- 

 mations are referable to causes that 

 are still in daily action, and they 

 may, by careful investigation, be 

 always distinguished from the gra- 

 vel which is strictly diluvian, as 

 the latter may be distinguished 

 from those more completely rolled 

 pebble beds of antediluvian origin 

 that occur among the regular strata 

 which compose the crust of our. 

 globe. 



A'LMANDINE. A precious stone, hav- 

 ing some of the characters of the 

 garnet. Almandine is much valued 

 as a precious stone, its principal 

 colour is red of various shades, 

 having sometimes a tinge of yellow 

 or blue, or a smoky aspect. Sp. 

 gr. 4 '3, and it is fusible into a 

 black enamel. The most beautiful 

 are brought from Sirian, the capital 

 of Pegu. 



A'LPINE. (alpinus, Lat.) This term 

 is not confined merely to the Alps, 

 and the things therewith connected, 

 but is applied to any lofty or 

 mountainous country, and to the 

 productions of elevated situations. 



ALTE'HNATE. (alternus, Lat.) Being 

 by turns; one after another; re- 

 ciprocal. In botany, applied to 

 leaves when they stand singly on 

 the stem or branches, alternately 

 first on one side, then on the other; 

 to branches when placed round the 

 stem alternately, one above the 

 other ; to flowers placed in regular 

 succession, one above another. 



ALTI'METEK. (from altus, Lat. and 

 perpov, Gr.) An instrument by 

 which the heights of bodies may be 

 ascertained. 



ALTI'METRY. (altimitrie, Fr. alti- 

 metria, It.) The art of measuring 

 altitudes or heights, whether ac- 

 cessible or otherwise. 



