cavern, mouths of iron--some of them caverns themselves--open upon you. This is the only portion of the contour of the place that an assailant could approach or batter. With a sufficient garrison, and superiority at sea, so as to throw in provisions, the place is clearly impregnable. The breaching batteries would have to be advanced beyond the guns on the northern portion of the rock, and the advanced works would be looked into, and down upon. In no sieges had either breach been attempted, or third parallel drawn. The batteries on the crest of the Rock, termed Willis’s, were the effectual defence, by their plunging fire into the Spanish works. The siege, properly speaking, was an attempt to starve, by cutting off supplies at sea, and to break down by sheer superiority of fire and shelling. The operations from the sea would have been successful but for the red-hot shot. The vaunted galleries have been constructed since the siege, and are mere matters of ostentation. Gibraltar has neither dock nor harbour. The Bay and anchorage are commanded by the Spanish forts, St. Barbara and St. Philip. These are levelled at present; but they will arise on the only occasion that we can require protection--that is to say, a war with Spain. They, therefore, must be restored in the mind’s eye, if you would form any estimate of the value of this fortress in case of war. They were dismantled during the late war by the Spanish government, lest the French _should occupy them_, and destroy the English shipping. The Spanish government, however, formally reserved its right to rebuild them. The question has been lately raised by our sinking one of their men-of-war in their own waters, while pursuing a smuggler. The guns of St. Barbara command the anchorage and batter the harbour; the shells from it and St. Philip pass clean over the Rock, lengthways, and can be dropped into every creek where a shoulder of rock might shelter a vessel from the direct fire. During the siege by France and Spain, the post was of no use. Unless when superior at sea, we had to sink our vessels to save them. In Gibraltar, there is little trade except contraband; the natural commerce having been systematically discouraged, that the martial departments might not be troubled, and with the view of reducing it to a mere military establishment. The fiscal regulations of Spain, which sustain this traffic, would long since have fallen but for its retention by England. We, therefore, lose the legitimate trade of all Spain for the smuggling profits (which go to the Spaniards) at this port.