Geosyncline a part of the earth crust that sank deeply through time. Its length may extend for several thousand kilometres and may contain sediments thousands of metres thick, representing millions of years of deposition. A geosyncline generally forms along continental edges, and is destroyed during periods of crustal deformation, which often produces folded mountain ranges. Bengal Geosyncline is one of the world's largest geosyncline that includes the bengal basin and the bay of bengal. The evolution of the Bengal Basin started in the Permo-Carboniferous with the sedimentation in the faulted Gondwana Basins. The break up of the Gondwanaland in the Cretaceous Period and the marine transgression led to the sedimentation in the Bengal Geosyncline. Since the Cretaceous Period, sedimentation in the Bengal Basin has been controlled by the movement of the Indian Plate with the Burmese and Tibetan plates and by the uplift of the himalayas and Indo-Burmese mountain ranges. [ASM Woobaidullah]