On the 19th, we persuaded sir Allan to lanch his boat again, and go with us to Icolmkill, where the first great preacher of Christianity to the Scots built a church, and settled a monastery. In our way we stopped to examine a very uncommon cave on the coast of Mull. We had some difficulty to make our way over the vast masses of broken rocks that lie before the entrance, and at the mouth were embarrassed with stones, which the sea had accumulated, as at Brighthelmstone; but, as we advanced, we reached a floor of soft sand, and, as we left the light behind us, walked along a very spacious cavity, vaulted over head with an arch almost regular, by which a mountain was sustained, at least a very lofty rock. From this magnificent cavern, went a narrow passage to the right hand, which we entered with a candle; and though it was obstructed with great stones, clambered over them to a second expansion of the cave, in which there lies a great square stone, which might serve as a table. The air here was very warm, but not oppressive, and the flame of the candle continued pyramidal. The cave goes onward to an unknown extent, but we were now one hundred and sixty yards under ground; we had but one candle, and had never heard of any that went farther and came back; we, therefore, thought it prudent to return. Going forward in our boat, we came to a cluster of rocks, black and horrid, which sir Allan chose for the place where he would eat his dinner. We climbed till we got seats. The stores were opened, and the repast taken. We then entered the boat again; the night came upon us; the wind rose; the sea swelled; and Boswell desired to be set on dry ground: we, however, pursued our navigation, and passed by several little islands in the silent solemnity of faint moonshine, seeing little, and hearing only the wind and the water. At last, we reached the island, the venerable seat of ancient sanctity; where secret piety reposed, and where falling greatness was reposited. The island has no house of entertainment, and we manfully made our bed in a farmer's barn. The description I hope to give you another time. I am, &c. XXVII.--To MRS. THRALE. Edinburgh, Nov. 12, 1773.