The present mill, however, is not on the actual site of Chaucer's, which stood some quarter of a mile higher up the stream. Its mill-pool still exists, and is famed as "Byron's Pool." Hither the poet used constantly to make his way when an undergraduate, as a retired spot where he might enjoy his favourite delight of bathing, which even in his day was a practice somewhat frowned upon by the academic authorities. A century or so earlier, as has been already said, any student found guilty of it was publicly flogged in the Hall of his College.[164] It is a fascinating place, overhung by fine trees, and remained in favour as a bathing-place even to the middle of the nineteenth century. Now it has become so silted up as to be practically useless. But on the river above it there is still a good swimming reach, little used, however, as most students are content with the University bathing sheds between Grantchester and Cambridge. [Footnote 164: See p. 153. After this preliminary domestic castigation he was again flogged on the morrow in the University Schools by the Proctors. A second offence meant expulsion from the University!] The footpath past these sheds is a pleasant byway between the two places, through the green meadows along the riverbank, and so also is the river itself, hereabouts no more than the "brook" which Chaucer calls it. It is, however, by no means a water to be played with rashly, having a tortuous course full of deep holes, in which many lives have been lost. Indeed, no student is now allowed on this "Upper River," unless a certified swimmer. A third alternative route is afforded by the lane between Grantchester and Newnham. Though the southern half of this suburb is actually in Grantchester parish, the lane still runs through open fields, and Grantchester itself is in no sense suburban. A strangely zig-zag road (with no fewer than four right-angle bends to left and right alternately in as many hundred yards), climbs from the mill to the church, which stands, like Trumpington, on the gravel terrace above the river. These river gravels are amongst the most interesting of Cambridgeshire geological formations. Not only does their height above the present stream level (sometimes as much as thirty feet) point to an age when the rivers must have been much larger than now, but they are prolific in organic remains, indicating, sometimes a warmer, sometimes a colder climate than ours. Here, at Grantchester, bones of the mammoth and of the woolly rhinoceros connote subarctic conditions; but a few miles further up the Cam, at Barrington, the terrace is full of hippopotamus, along with elephant and rhinoceros of African type, postulating a sub-tropical temperature.