 On 9 January 1834, further south, they reached Port St Julian and exploring the local geology in cliffs near the harbour Darwin found fossils of pieces of spine and a hind leg of "some large animal, I fancy a Mastodon".On 26 January they entered the Straits of Magellan and at St. Gregory's Bay they met half-civilised Patagonian "giants" over tall, described by Darwin as "excellent practical naturalists".One told him that the smaller rheas were the only species this far south, while the larger rheas kept to the north, the species meeting around the Rio Negro.