fuller.] COLLECTION OF WELL RECORDS AND SAMPLES. 33 
Names of owners and drillers who furnish records and samples will appear in the 
annual publication of the Geological Survey on well borings. 
The Survey desires to assist and cooperate with owners and drillers in every way 
possible, and will be glad to answer questions. 
To assist the driller in identifying the rocks, in obtaining a correct 
understanding of simple geologic conditions, and in keeping more 
intelligent records, a few geologic notes and definitions of the more 
common types of rocks, based largely on notes by Mr. G. H. Eldridge, 
are printed on the inside of the back cover and on the page facing it, 
respectively. These are given below. 
Geologic notes. 
In a simple classification rocks may be grouped into three divisions: (1) Sedimen- 
tary, (2) metamorphic, and (3) igneous. 
Sedimentary rocks. — Sedimentary rocks are formed of fragments worn from older 
rocks by the action of rain, wind, frost, etc. Such materials were carried by water 
or glaciers until deposited as beds of clay, sand, gravel, marl, etc. Other deposits 
consist largely of corals, or of shells, such as oysters and clams. When first deposited 
the materials are loose and unconsolidated, but they become gradually hardened and 
cemented together, especially when covered by later beds, and form solid rocks. 
Metamorphic rocks. — Sedimentary rocks have frequently been subjected to heat and 
pressure, which has further hardened them, or even produced a crystalline texture. 
Sediments and igneous rocks so altered are known as metamorphic rocks. Mica- 
schist and marble are typical examples. They generally retain a bedded or foliated 
structure. 
Igneous rocks. — Igneous rocks have come from the earth's interior in a molten state 
and have forced their way between other rocks or have overflowed as lava beds at 
the surface. They are nearly all more or less crystalline in texture. 
Resemblance of rock* of different ages. — Rocks of the types indicated above occur the 
world over, those of one locality often being indistinguishable from those of another. 
: Notwithstanding this, there may be a difference of thousands of years in age and a 
great variance in conditions of formation. It is not warrantable, therefore, to say 
that because a rock in California has the same composition as an oil-bearing rock in 
Ohio it is of the same age and will yield petroleum. 
Fossils. — In sedimentary rocks remains of animals and plants are often found. 
These generally consist of portions or impressions of shells, skeletons, or leaves, and 
are known as fossils. A bed can frequently be recognized and its age determined by 
fossils. It is of great importance that all fossils be saved. 
Definition of a formation. — A rock or succession of rocks possessing uniformity of 
character throughout a considerable area is termed a formation, and is given a name, 
such as Trenton limestone, etc. The importance of identifying these is great, and 
their identification will be much facilitated by the preservation of samples. 
Structure — When deposited, sedimentary bedsare nearly horizontal. Subsequently 
they have often been thrown into inclined positions or bent into wave-like folds, the 
arches of which are known as anticlines and the troughs as sijnclines. When the beds 
are further disturbed they may become broken and the different parts displaced or 
faulted from their original position. The slope of the beds is known as the dip, and 
the direction in which they extend or would outcrop on a horizontal surface is known 
as the strike. The directions of strikes and dips are of importance in studying the 
occurrence of water and oil, and should be recorded whenever possible. 
Bull. 264—05 3 
