From Silhet we took large boats to navigate the Burrampooter and Megna, to their embouchure in the Bay of Bengal at Noacolly, a distance of 250 miles, whence we were to proceed across the head of the bay to Chittagong, about 100 miles farther. We left on the 7th of December, and arrived at Chattuc on the 9th, where we met our Khasia collectors with large loads of plants, and paid them off. The river was now low, and presented a busy scene, from the numerous trading boats being confined to its fewer and deeper channels. Long grasses and sedges (_Arundo, Saccharum_ and _Scleria_), were cut, and stacked along the water's edge, in huge brown piles, for export and thatching. On the 13th December, we entered the broad stream of the Megna. Rice is cultivated along the mud flats left by the annual floods, and the banks are lower and less defined than in the Soormah, and support no long grasses or bushes. Enormous islets of living water-grasses (_Oplismenus stagninus_) and other plants, floated past, and birds became more numerous, especially martins and egrets. The sun was hot, but the weather otherwise cool and pleasant: the mean temperature was nearly that of Calcutta, 69.7 degrees, but the atmosphere was more humid.* [The river-water was greenish, and a little cooler (73.8 degrees) than that of the Soormah (74.3 degrees), which was brown and muddy. The barometer on the Soormah stood 0.028 inch higher than that of Calcutta (on the mean of thirty-eight observations), whereas on the Megna the pressure was 0.010 higher. As Calcutta is eighteen feet above the level of the Bay of Bengal, this shows that the Megna (which has no perceptible current) is at the level of the sea, and that either the Soormah is upwards of thirty feet above that level, or that the atmospheric pressure there, and at this season, is less than at Calcutta, which, as I have hinted at chapter xxvii, is probably the case.] On the 14th we passed the Dacca river; below which the Megna is several miles wide, and there is an appearance of tide, from masses of purple _Salvinia_ (a floating plant, allied to ferns), being thrown up on the beach like sea-weed. Still lower down, the vegetation of the Sunderbunds commences; there is a narrow beach, and behind it a mud bank several feet high, supporting a luxuriant green jungle of palms (_Borassus_ and _Phoenix_), immense fig-trees, covered with _Calami,_ and tall betel-palms, clothed with the most elegant drapery of _Arostichum scandens,_ a climbing fern with pendulous fronds.