GEOLOGY and EARTH SCIENCE

Introduces glaciers, fossils, rock formation
and erosion, geological structures, plate
tectonics, evolution, atmospherics, astron-
omy & space science. Very rich resource
material, some at OVER 50% DISCOUNT!

CONTINENTAL DRIFT & PLATE TECTONICS
Reviews the theories and supporting research evidence for these highly influential concepts that explain so much. 3 programs. 58 slides and guides.
EP #310X SLIDES
$99.95

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SAVE OVER $27.00 ON 3 SLIDE SET BUNDLE ORDER EP #310X.......$99.95
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PLATE TECTONICS AND THE SPREADING SEA FLOOR Slides order #310 ........$42.50

Block diagrams, maps and cross-sections are used to depict the movements of
the earth's tectonic plates. Special emphasis is given to the igneous activity, rock types
and structures of convergent and divergent plate boundaries. Color photographs depict
features along the only on-land plate boundary in North America, the San Andreas fault,
in California. 2O slides and guide.

CONTENT SAMPLE: 20584 Internal Structure of the Earth--A Cross Section. The
internal zones of the earth are shown here: the core, mantle, crust, lithosphere and asthen-
osphere.

The outer part of the core is thought to be fluid, but it is under such great pressure that it
probably is not as fluid as water. It probably consists of an alloy of two metals, nickel and iron.
The central portion is thought to be solid.

The boundary between the core and the overlying mantle is located 2,900 km (1,800
miles) below the surface.

The crust of the earth, which is the outer, rigid, thin skin, consists of light rock with a
specific gravity of about 2.5. In ocean basins the crust is about 5 km (3 miles) thick, while in
continental areas it ranges up to a thickness of 55 km (35 miles). Recent geophysical
investigations have led to the discovery of a new zone in the upper mantle, the so-called
asthenosphere. This is apparently a somewhat weak and plastic shell over which the rigid outer
shell, called the lithosphere, floats. The outer lithosphere is about 100 km (60 miles) thick and the
underlying asthenosphere ranges from 100 to more than 250 km (60 to 155 miles) below the
surface. According to the plate theory, the outer lithosphere is broken into plates that float and
move inexorably over the asthenosphere.

Most of the evidence for the internal constitution of the earth comes from the study of
earthquake waves. These are shocks or vibrations generated during a quake.

REVIEWS: "Well done diagrams, maps, and cross sections as well as color
photographs.... These would be excellent as a first purchase..." Previews.
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THE DRIFTING OF THE CONTINENTS Slides order #308 ........$42.50

Presents the theory of Continental Drift with sketches of the position of the
continents over time, and its relationship to the later theory of plate tectonics. Land
formations produced by continental movement are illustrated; as is the span of geologic
time and representative life forms of the various periods. 2O slides and guide.

CONTENT SAMPLE: 2. Paleoclimatic indicators suggest that the continents were in
different positions in the past. If, during the late Paleozoic Era, the continents were in the position
that Wegener postulated, then the southern hemisphere continents (collectively called
Gondwanaland) would have been at or near the South Pole; thus, we should expect evidence of
glaciation. This is exactly what was found in the late Paleozoic deposits of South America, India,
Africa and Australia. The evidence is in the form of glacial tillites, heaps of glacially scratched
boulders and cobbles imbedded in unstratified beds of sand and clay. Moreover, tillites are
interbedded with other layers of sediment that contain fossils indicative of late Paleozoic age.

REVIEWS: "...text is well-written and provides background information and definitions to
help those not familiar with some geologic terms...the photographs are very good." Previews.
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CONTINENTAL DRIFT Slides order #SS-0300S ........$42.50

A mini-voyage into the theory's background and basics of current tectonic theory.
18 frames and guide. (Filmstrip order #SS-0300F ...........$15.00)

CONTENT SAMPLE: 16. The recent discovery of paleomagnetic rocks provides some
clues to the puzzle. Magnetic particles trapped in prehistoric lava flows aligned with the magnetic
poles. The fact that many such particles point in directions further than the limits of polar variance
confirm that continents have moved. Whether continents moved with respect to each other (which
would settle the crust movement theory) is not yet clear. Analysis so far indicates that India,
Africa, and Australia have all moved northward.
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seafl02t.tif Earth's continental jigsaw puzzle. graphic by Educational Images Ltd.

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