From having no sandbar at its mouth like the Mersey outside of Liverpool, it is navigable for sea vessels to London bridge, a distance of forty-five miles from the Nore, or nearly a fourth of its entire length. The area of the basin drained by the Thames is estimated at about six thousand five hundred miles. The progress of half a century has made wonderful changes in the river. Wharves have taken the place of trim gardens, and the dirty coal scow is now found where the nobleman's state barge formerly anchored. No man, it is said, can count the national debt of England, but who can give an adequate idea of the number of millions of tons that annually pass through this highway? The flow of land water through Teddington Weir is annually 800,000,000 gallons. This is the main body of the river within the metropolitan area, not counting the additions it receives from rain-falls and other sources. Since the removal of the old London Bridge, the tide has been lower upon an average. Shoals have been brought to light, before unknown, and the result has been that nothing but a most constant and unremitting dredging has enabled the Thames Conservancy Board to keep the river navigable. It requires but a glance at Blackfriar's Bridge to determine how much longer it will take to remove all the gravel from the bed of the river, and leave the solid London clay as its bed. Every old bridge when removed leaves so many tons of gravel which eventually finds its way to the mouth of the Thames, and there forms shoals. The channel of the river thus deepened, becomes more and more brackish every year, and it can be but a question of time, as to how and from what source the inhabitants are to derive their water supply for drinking purposes. At the East India Docks the tide falls fourteen inches lower than formerly, and it is a fact that the low water at London Docks is lower than the low water at Sheerness, sixty miles below. At present the tide at London Bridge has a rise of 18 feet. This river at almost any tide can float the largest ships, being 33 feet in depth at London Bridge. The river water when found at low tide near the city is much prized for its power of self-purification, and is much in requisition for sea voyages, for the reason that it contains so large a percentage of organic matter. There are few or no fish to be found in the Thames in the neighborhood of the city or below, owing to the impurities prevailing from drainage and sewage. This fact is particularly to be noticed in the vicinity of the town of Barking on the Thames, where is located the outfall for all the sewage of dirty London. Formerly salmon were very plentiful at the Nore, and the last one there caught sold at fifteen shillings per pound.