Memoirs of the Geological Survey of India . may be seen in many examples :—hand specimens, notmore than 6 inches square, often exhibit one half the bedded, and one half the zig-zag struc-sture.* The mineral which determines the formation of the latter is carbonate of lime. Shalesof this character occur largely in some parts of the Ootatoor Group, and to some extent also inthe Trichinopoly Group, especially in the neighbourhood of Alundanapuram. I have noted themon the map as the zig-zag shales. Another lithological peculiarity of similar origin, and occur-ring in association with the above, is
Memoirs of the Geological Survey of India . may be seen in many examples :—hand specimens, notmore than 6 inches square, often exhibit one half the bedded, and one half the zig-zag struc-sture.* The mineral which determines the formation of the latter is carbonate of lime. Shalesof this character occur largely in some parts of the Ootatoor Group, and to some extent also inthe Trichinopoly Group, especially in the neighbourhood of Alundanapuram. I have noted themon the map as the zig-zag shales. Another lithological peculiarity of similar origin, and occur-ring in association with the above, is a shale of loose porous structure, formed oflayers of impure fibrous carbonate of lime, with a general horizontal aiTangement, whichare piled loosely on one another so as to leave the mass full of lenticular cavities of Concretions. all sizes. A third peculiar lithological form due to the crystal- lization of impure carbonate of lime is that of large concretions (Fig. 7), the surfaces of whichFig. 7. Large Concretion in Ootatoor
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Keywords: ., bookcentury1800, booksubjectgeology, booksubjectminesandmineralr
