Baid low lying, narrow winding valley, ridged by relatively high topography. This type of topography, locally called chala, is commonly seen in the dhaka, gazipur, tangail, mymensingh and jamalpur red soil areas (ie within the madhupur tract). The valleys are believed to be the remnants of the past estuarine tidal channels when the area had a estuarine environment during the Pleistocene period (about 0.8-1 million years ago). As the sea receded south and the area became uplifted, the baids lost connection with their parent channels, thus becoming inoperative. In most cases, the baids become well connected with the parent channels during the monsoon when they receive a flow from outside and act as local drainage outlets as well as a sink for the washed out eroded soil of the adjoining chalas. In the dry season it is primarily used for boro rice cultivation. The soils of the baids are mostly silt-clay to clay and rich in organic matter. [Mohd Shamsul Alam]