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By birth? i think? do you mean like how did they get in a certain caste? because then it would be by birth. but if you mean like what were the castes, i forget.
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Sedimentary rocks form beneath the surface of the earth. 
Mummified fossils are commonly found in cold climates. 
<em>[ They are formed when remains are buried rapidly in dry cold or hot environments ]</em>
A. A pilgrimage to Mecca.