As surveys were still in progress, Darwin set off on another "galloping" trip in Banda Oriental to see the Uruguay River and visit the Estancia of Mr Keen near Mercedes on the Río Negro. On 25 November, he "heard of some giants bones, which as usual turned out to be those of the Megatherium" but could only extract a few broken fragments. The next day, he visited a nearby house and bought"a head of a Megatherium which must have been when found quite perfect" for about two shillings, though the teeth had since been broken and the lower jaw had been lost. Mr Keen arranged to ship the skull downriver to Buenos Aires. At Las Piedras, a clergyman let him see fossils, including a club-like tail which he sketched and called an "extraordinary weapon". His notes included a page showing his realisation that the cliff banks of the rivers exposed two strata formed in an estuary interrupted by an undersea stratum, indicating that the land had risen and fallen.