Capt. A. Gerard, from whose letters on a survey of the middle valley of the Setlej, in the year 1818, a brief sketch of the geology of that part of the Himálaya was prepared, which has been inserted in the Geological Transactions (1st vol., New Series), has since continued to explore the same interesting portion of the great Indian chain of mountains. A short narrative of a visit to the same quarter, in 1820, was communicated to the Royal Society of Edinburgh, and is published in the 10th volume of the Edinburgh Philosophical Journal, (page 295.) In the subsequent, year (1821) Capt. A. Gerard, with his brother, Mr. J. G. Gerard, more fully explored the same valley, to complete a geographical survey of it. Their diary, and the geological specimens collected by them, have, at their request, been freely communicated to me by the East-India Company, with the liberal permission of retaining a duplicate set of the specimens. This I accordingly have had the satisfaction of presenting to the Geological Society. But, as the diary contains particulars unconnected with geology, yet not devoid of interest in a more general view, I now offer to the notice of the Royal Asiatic Society a summary of it, interspersed with remarks, and including extracts of the more important passages.