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A       D I V I S I O N      O F      E K L A V Y A      E D U C A T I O N      F O U N D A T I O N    Code: TLM-Sc-004 Age: 9-16 yrs    Name: Geology Demonstration Kit   they are composed of less dense rocks. If materials (sediments) are removed from a mountainous area by erosion and are deposited in an adjacent shallow sea, the areas are no longer balanced and the highland will slowly rise and the lowland will sink as they adjust to the new conditions. These movements or adjustments probably take place ad depth where the rocks are under great pressure and can flow plastically. The following diagram shows these relationships in a generalized fashion. ACTIVITY TO DEMONSTRATE ISOSTASY To demonstrate this theory, fill the tray with water and place two of the white styrofoam blocks on the water. Using a spoon, place several teaspoonsful of sand on one of the blocks. The water represents the denser rocks of the ocean basins and the two blocks represent continents "floating" on the denser rocks (water). The block with sand represents a "highland" and the other block a "lowland" or basin of deposition. Carefully place sand from the "highland" block onto the "lowland" block. Notice how the level of the "highland" block rises as sand (eroded materials) is removed and placed on the "lowland" block. Note also the compensatory movement of the "lowland" block. It sinks as sand (sediments) is placed upon it.     Discussion: 1. What would happen to the continents if they did not rise isostatically after erosion? 2. What will happen to the earth's surface in the area where a large continental glacier is present? 3. What will happen when the glacier melts? 4. Is there any evidence that this happened in India or Asia during the Ice Age? Superposition: In a sedimentary rock, layers are deposited one above the other. The first layer will be the oldest. The recently formed layer will be the youngest and superimposed on the older beds. Here layer 3 is the youngest. In other words, as sedimentary rocks accumulate, the younger layers are deposited on top of older rock layers. This principle can be demonstrated with the three foam pieces:    In areas of deformation (folding and faulting), the principle cannot always be applied directly. This can be demonstrated as follows: 2. Fold the foam pieces as shown and label them 1, 2 and 3 as before. Point out to the class that now the oldest rock layer (3) rests on top of a younger rock layer (2) and layer 2 on top of 1. This situation occurs when rock units are overturned as shown by the foam pieces.

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