34 RECORD OF DEEP WELL DRILLING FOR 1904. [bull. 264. 
The definitions of rocks are as follows: 
In order to assist the driller in keeping records, brief definitions of the more com- 
mon rock terms are given below. 
UNCONSOLIDATED DEPOSITS. 
Soil and subsoil. — The weathered upper portions of any rocks. 
Till. — An irregular mixture of clay, sand and bowlders deposited by glaciers. 
Alluvium. — Sand, clay, etc., deposited by streams. 
Gravel, sand, and clay. — Made up respectively of pebbles, sand grains, and liner 
particles. 
( 'halk. — A soft, white earthy substance made up of fine particles of lime. 
Marl. — A clayey substance containing much lime. 
SEDIMENTARY ROCKS. 
Sedimentary rocks are made up of fragments of older rocks. The fragments or 
grains are usually rounded, a feature which helps to distinguish them from igneous 
rocks. 
Conglomerate. — Consolidated gravel . 
Sandstone. — A consolidated sand. It is said to be massive if there are few bedding 
planes, and shaly if it splits into plates. 
Quartzite. — A sandstone in which the spaces between the grains have filled with a 
hard cement (silica), forming an excessively hard rock. 
Shale.— Consolidated clay; a soft, tine-grained rock which tends to split into thin 
plates (often improperly called soapstone). 
Slate. — Like shale, but harder; splits into thin plates which mayor may not coincide 
with the bedding. The tendency to split is not often recognized in drilling. Example 
Roofing slate. 
Limestone. — Formed from consolidated marly beds, or from beds of coral, shellfish, 
etc. It is composed mainly of carbonate of lime, but often contains sand and other 
impurities, and is often very hard. It can be most readily detected by the bubbling 
which takes place when it is touched with muriatic acid. 
Flint, me/: salt, gypsum, coal. — These are too well known to require definition. 
Concretions. — Hardened lump-like masses within the rock, and should not be con- 
founded with real bowlders. 
METAMORPHIC AND IGNEOCS ROCKS. 
These rocks are generally made up of angular crystals, often recognizable by their 
glistening faces, a feature which is not often possessed by the fragments of sedimen- 
tary rocks. 
Marble <tn<i dolomite. — Marble is a cystalline limestone and gives the same reaction 
with acid as limestone, marl, and chalk. Dolomite resembles limestone, but the bub- 
bling with acid takes place only when the acid is hot. In composition it differs from 
limestone and marble in that it contains carbonate of magnesium. 
Soapstone or talc. — Fairly soft and greasy to the touch. It is seldom encountered 
in drilling, the substance called soapstone usually being a soft shale, although the 
name is sometimes incorrectly applied to clay or slate. 
Schist. — A crystalline rock characterized by thin layers of mica or other mineral. 
Gneiss. — A rock intermediate in character between schist and granite. 
Granite. — A crystalline rock composed of quartz, feldspar, and other minerals. 
Trap. — A very dark crystalline rock of igneous origin. 
