Early traditions in urban ecology and social area analysis have recently converged in the approaches of factorial ecology. Comparison of factorial ecologies undertaken in recent years throughout the world enables a list of the necessary and sufficient conditions for ecological differentiation of urban subpopulation by social rank, stage in life Cycle, and ethnic segregation to be specified. At the same time, a more traditional comparative literature suggests widely different ecologies of pre-industrial, industrial, and post-industrial cities. This study attempts to initiative systematic cross-cultural ecological analysis by means of a structured factorial ecology of Calcutta. The investigation reveals an interpenetration of pre-industrial and industrial ecological components, consistent with notions that city is in some transitional developmental stage. At the same time, the changing significance of caste in ordering Indian society is revealed.