387 



Alhivium. Recent deposits of earth, sand, gravel, mud, stones, peat, 

 shell-banks, shell marl, drift-sand, &o., resulting from causes now inac- 

 tion. This term is gHnerally applied to those deposits in which water 

 is the principal agent. 



Alum-rocks. Rocks which, by decomposition, form alum. 



Amorphous. Bodies devoid of regular form. 



Amijgdahid. A trap rock which is porous and spongy, with round- 

 ed cavities scattered through its mass. Agates and simple minerals are 

 ■often contained in these cavities. 



Anthracite. A species of mineral coal, hard, shining, black, and de- 

 void of bitumen. 



Anticlinal. An anticlinal ridge or axis is where the strata along a 

 line dip contrariwise, like the sides of the roof of a house. 



Arenaceous. Sandy. 



Argillaceous. Clayey. 



Augite. A simple mineral of variable color, from black through 

 green and gray to white. It is a constituent of many volcanic and 

 trap[)ean rocks, and is also found in some of the granit c rocks. 



Avalanche. This term is usually applied to masses of ice and snow 

 which have sliddi^i from the summits or sides of mountains. It is now 

 also applied to slides of eirth and clay. 



Basalt. One of the common trap rocks. It is composed of 

 augite and fe'dspar, is hard, compact, and dark green or black, and has 

 often a regular columnar aspect of triip rocks. The palisades of the 

 Hudson show the columnar aspect of trap rocks. The Giants' ('auf«e- 

 way is cited as an example of Basaltic rocks, and the columnar structure 

 is there very strikiugly displayed. 



Bitumen. Mineral pilch, which is often seen to ooze from fossil coal 

 when on fire. 



Bituminous Shale. A slaty rock, containing bitumen, and which 

 occurs in the coal measures. 



Blende. Suiphuret of zinc. A common shining zinc ore. 



Bluffs. High banks of earth or rm-k, with a steep front. The term 

 is generally applied to high banks forniing the boundaries of a river, or 

 river alluvions. 



Botryoidal. Resembling a bunch of grapes in form. 



Boulders. Rocks which have been transported from a distance, and. 



