(a) Relationship of Topography to Schist.
Landforms Developed in Areas of Schist. The landforms associated with schist in humid
climates consist of smooth, rounded hills with steep side slopes. These hills are covered with deep soil profiles
consisting primarily of well-drained, sandy silts and clays. In arid climates, there is a moderate, well-dissected
relief with rugged surfaces and a thin soil cover.
Drainage Developed on Schist. The foliated nature of schists is responsible for the
development of a medium- to fine-textured, rectangular dendritic drainage pattern in both humid and arid
climates. Many parallel, U-shaped gullies occur, attesting to the ease with which the sandy residual soils are
eroded.
Vegetation in Areas of Schist. The thick soils that develop over areas of schist in humid
regions may support abundant vegetation. The tops of the rolling hills are normally cultivated, while the steeper
side slopes remain forested. The vegetation on schist formations in arid regions is generally sparse, consisting of
scattered grasses and scrub brush, with minor concentrations centered around areas of deeper soils or higher
moisture.
(b) Engineering Properties of Schist. The tendency of schist to split into thin flakes makes it
hazardous to excavate and undesirable as construction material. However, some higher-grade schists may be used
for fills or base courses or as aggregate for portland cement.
(3) Gneiss. As heat and pressure steadily increase, schists begin to grade into gneiss, a rock representing
the highest degree of regional metamorphism. Gneiss is a coarse-grained metamorphic rock made up of
alternating layers of light and dark minerals that impart a banded appearance to hand specimens. Sometimes,
banding is observable on a regional scale also, but it is often subdued. Planes of weakness along the banding
allow the rock to be split into flat sheets, indicating that gneiss is a foliated metamorphic rock, although the
foliation is not as well developed as it is in shale or schist. Where the ground surface is visible through the
vegetation, a uniformly light photo tone is apparent on aerial photographs.
(a) Relationship of Topography to Gneiss.
Landforms Developed in Areas of Gneiss. Landforms eroded from massive bodies of gneiss
will generally consist of sharp, steep hills with parallel ridges, resulting from the differential weathering of the
various minerals that make up the banded structure.
Drainage Developed on Gneiss. The landforms produced by the differential weathering of
this foliated rock control the drainage system that normally has a fine- to medium-textured, angular dendritic
drainage pattern. Often, only a thin soil cover develops on gneissic terrane, but where soils are deep, U-shaped
gullies will form, indicating that the underlying material is composed of a moderately cohesive sand-clay mixture.
Vegetation in Areas of Gneiss. The thin residual soils that form on gneiss in all types of
environments will usually support only a natural vegetative cover. In humid climates, these regions are forested;
in arid climates, scrub and grass cover dominate, especially in valleys where soil depths are greater and more
moisture is available.
EN5341
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