In the country of Kattaun, near the head of Urei River, there are extensive caves (goha) from the soil of which saltpetre (mesiyu mantah) is extracted.  M. Whalfeldt, who was employed as a surveyor, visited them in March 1773.  Into one he advanced seven hundred and forty-three feet, when his lights were extinguished by the damp vapour.  Into a second he penetrated six hundred feet, when, after getting through a confined passage about three feet wide and five in height, an opening in the rock led to a spacious place forty feet high.  The same caves were visited by Mr. Christopher Terry and Mr. Charles Miller.  They are the habitation of innumerable birds, which are perceived to abound the more the farther you proceed.  Their nests are formed about the upper parts of the cave, and it is thought to be their dung simply that forms the soil (in many places from four to six feet deep, and from fifteen to twenty broad) which affords the nitre.  A cubic foot of this earth, measuring seven gallons, produced on boiling seven pounds fourteen ounces of saltpetre, and a second experiment gave a ninth part more.  This I afterwards saw refined to a high degree of purity; but I conceive that its value would not repay the expense of the process.

BIRDS-NEST.

The edible birds-nest, so much celebrated as a peculiar luxury of the table, especially amongst the Chinese, is found in similar caves in different parts of the island, but chiefly near the sea-coast, and in the greatest abundance at its southern extremity.  Four miles up the river Kroi there is one of considerable size.  The birds are called layang-layang, and resemble the common swallow, or perhaps rather the martin.  I had an opportunity of giving to the British Museum some of these nests with the eggs in them.  They are distinguished into white and black, of which the first are by far the more scarce and valuable, being found in the proportion of one only to twenty-five.  The white sort sells in China at the rate of a thousand to fifteen hundred dollars the pikul (according to the Batavian Transactions for nearly its weight in silver), the black is usually disposed of at Batavia at about twenty or thirty dollars for the same weight, where I understand it is chiefly converted into a kind of glue.  The difference between the two sorts has by some been supposed to be owing to the mixture of the feathers of the birds with the viscous substance of which the nests are formed; and this they deduce from the experiment of steeping the black nests for a short time in hot water, when they are said to become white to a certain degree.  Among the natives I have heard a few assert that they are the work of a different species of bird.  It was also suggested to me that the white might probably be the recent nests of the season in which they were taken, and the black such as had been used for several years successively.  This opinion appearing plausible, I was particular in my inquiries as to that point,