About five-and-twenty years ago a large boulder, lying in the garden of Wimpole Hall, near Koyston, was pointed out to the Rev. Osmond Fisher by the Lady Hardwicke of that period, and s-he informed him that it had been brought from near Old North Eoad Station when the hill there was lowered. As its dimensions and nature had not been determined, Mr. Fisher invited me to accompany him to Wimpole on April 22nd in order to examine it, having previously obtained permission from the present owner of the property, Lord Eobartes. After a brief search the boulder was discovered lying about 30 yards north-west of the conservatory and almost concealed under a dense growth of ivy. It measures approximately 8 ft. 10 in.inlength, 4 tt.inheight, and lft. 8 in.inbreadth, and consists of a greenish-grey tough sandstone. Mr. Fisher determined its S.G. to be 191 and its weight to amount to 3 tons 2cwt. Lithologically the rock is precisely similar to portions of the Spilsby Sandstone of Lincolnshire, and a specimen in the Woodwardian Museum from near Claxby is indistinguishable from it. By good luck a small Ammonite occurred in a fragment chipped off by the Kev. E. Conybeare, who met us at Wimpole; and Mr. G. C. Crick, of the British Museum, who has kindly examined it for us, writes that it ia “ not referable to any species which has hitherto been recorded from Great Britain, “but that it” is closely related to Olcosteyhanus (Craspedites) subdilus (Trautschold), which has been recorded from the Spilsby Sandstone of Lincolnshire (Pavlow and Lam pi ugh, ‘Argiles de Speetpn,’ etc., p. 116, pi. xiii (vi), figs. 5a, b, c).“