Essential of Geology , 2 ed.

(5.1) What a Geologist Sees: Contact between Basement and Cover

Near the bottom of the Grand Canyon, we can see the boundary between the sedimentary veneer, or cover (here, a succession of horizontal layers), and the older basement (here, the steep cliff of dark metamorphic rock that goes down to the river). A geologist’s sketch emphasizes the contact, or boundary, between cover and basement.

(5.2) What a Geologist Sees: Formations in the Grand Canyon

In this photo of the Grand Canyon, we can see five formations. Formations and groups are examples of stratigraphic units. Note that each formation consists of many beds, and that beds range greatly in thickness. The boundaries between units are called “contacts.”

(5.3) Formation of Cross Beds

When blowing sand builds into sand dunes in a desert, the sand tumbles up the windward side of the dune, and settles in quieter air on the leeward side. This animation shows how cross beds develop during the deposition of sediment.

Created by: Stephen Marshak

(5.4) What a Geologist Sees: Crossbeds

On this cliff face of sandstone in Zion National Park, we see remnants of ancient sand dunes. Cross beds indicate the wind direction during deposition.

(5.5) Transgression and Regression

This animation demonstrates the Doppler effect as applied to light by simulating the effect of a star's velocity upon the starlight as viewed from Earth. Use the horizontal scrollbar to change the star's velocity. Notice the red shift as the star recedes from you, and the blue shift as it moves toward you. The greater the star's speed, the greater the spectral shift.

Created by: Stephen Marshak

(5.6) What a Geologist Sees: Channel Deposits

This exposure shows the lens-like shape of an ancient gravel-filled river channel in cross section. A geologist's sketch emphasizes the channel shape.