Abstract
The paper records the occurrence of stromatolitic structures, ascribed to the algal genus Collenia, from the dolomitic limestone of Pithoragarh, U. P. Overlying this limestone is an extensive band of magnesite. It is tentatively suggested that the magnesite deposit is the result of primary precipitation of magnesium carbonate, aided by the activity of algae.
The limestones, dolomitic limestones, shales and slates, including the stromatolite-lime. stone and magnesite beds constitute a distinct formation which may be designated as the Calc Zone of Pithoragarh. On the basis of lithology, stratigraphical position and the evidence of stromatolitic structure, this Calc Zone of Pithoragarh appears to be the equivalent of the Deoban limestone of the Chakrata area. It is not possible at this stage to state definitely, as to which specific geological period this zone belongs. It may, however, be stated with some confidence that it lies somewhere between Precambrian and early Ordovician.
