This file provides explanatory information for the 
database attributes used for the geologic map of the
Charleston, SC quadrangle.

ID:
Consecutively numbered units.

TYPE:
These unique designations are the geologic map symbols 
used for the various geologic units.  The upper-case 
letters refer to the general geologic ages of the 
units (Q=Quaternary, T=Tertiary).  The lower case 
letters refer to the name, specific age, and (or) 
facies of the geologic units (for example, 
Qhs=Quaternary+Holocene+barrier sands; Qwf=
Quaternary+Wando Formation+fossiliferous shelf 
sand).

UNIT:
Names of geologic units. Names with upper-case
letters are formally defined (for example, Wando
Formation).  Units with names using lower-case
letters are informally defined (for example,
Ten Mile Hill beds, artificial fill).

FACIES:
General statement of the depositional environment
and (or) lithology of a geologic unit.  FACIES 
represents the appearance and characteristics of a
sedimentary unit, typically reflecting the conditions
of its origin.

DEPOSITIONAL ENVIRONMENT:
Describes the environment in which the sediments
originally accumulated (for example, estuary,
barrier island, marine shelf).

RELATIVE AGE:
Age of the geologic units as identified on the
standard geologic time scale.  Defined in terms 
relative to other geologic units rather than in
terms of years.

MIN_AGE:
Approximate minimum ages of geologic units in
thousands of years.

MAX_AGE:
Approximate maximum ages of geologic units in 
thousands of years.

ABSOLUTE AGE:	
Ranges or values for approximate ages of geologic
units as determined from fossil ages, amino-acid
racemization ages, and (or) radiocarbon ages.
(ka=thousands of years, Ma=millions of years).

LITHOLOGY:
The physical characteristics of rocks or sediments
as seen in outcrops, hand samples, or subsurface 
samples.  Described on the basis of characteristics
such as color, mineralogic composition, and grain
size. 

Principal sediment types found in the geologic units.
Sands consist primarily of quartz grains between 
0.0625 mm and 2.0 mm. Silts consist primarily
of quartz grains between 0.0039 mm and 0.0625 mm.
Limestone/marl deposits consist of true limestone or
limy clay (marl).  Muck consists of variable 
percentages of sand, silt, and clay mixed with a
high percentage of fine-grained organic material.
Descriptions of sediments in the LITHOLOGY and 
MODIFIER sections are qualitative visual descriptions.

MODIFIER 1, 2, 3, 4
These descriptive terms modify the principal lithologic
terms.  Modifiers may refer to size of sand grains 
(for example, fine-medium), to admixtures of materials
of contrasting grain size (for example, silty, sandy, 
clayey), to special components (for example, 
fossiliferous, phosphatic), to grain-size sorting 
(for example, well-sorted, clean), or to 
stratification type or other fabric characteristics 
(cross-bedded, bioturbated).

Standard Geologic Grain Size Chart:
Gravel:  larger than 2.0 millimeters

Sand:
	Very coarse: 1.0 to 2.0 mm
	Coarse:  0.50 to 1.0 mm
	Medium:  0.25 mm to 0.50 mm
	Fine:  0.125 mm to 0.25 mm
	Very fine:  0.0625 mm to 0.125 mm

Silt:  0.0039 mm to 0.0625 mm

Clay:  smaller than 0.0039 mm

FRESH COLOR 1, 2
Dominant (1) and secondary (2) colors of sediments in
fresh exposures and subsurface samples.

WEATHERED COLOR 1, 2
Dominant (1) and secondary (2) colors of sediments in
weathered exposures.

COMPACTION
Qualitative field assessments of sediment compaction
stated as "loose", "moderate", or "dense".  Younger
sediments (Pleistocene and Holocene) tend to be 
loose or moderately compacted.  Older Eocene, 
Oligocene,and Miocene sediments tend to be dense 
relative to the younger deposits but still may be 
penetrated with a knife blade using moderate pressure.