Darwin at that time was exploring Patagonia which is the current day tip of Chile and Argentina. They were wending their way through the strait with it’s strange currents, cul de sac channels, and baffling winds. Few who haven’t been there understand the difficulties of threading your way through by sail, but it’s informative that the original passage of the strait by Magellan took 38 days. Due to the narrowness of the passage and the limited sea room clipper ships typically avoided the strait and instead passed South through the Drake passage.
Here’s the entry from his diary that day:
With very baffling winds we anchored late in the evening in Gregory Bay, where our friends the Indians anxiously seemed to desire our presence. During the day we passed close to Elizabeth Island, on North end of which there was a party of Fuegians with their canoe &c. They were tall men & clothed in mantles; & belong probably to the East Coast; the same set of men we saw in Good Success Bay; they clearly are different from the Fuegians, & ought to be called foot Patagonians. Jemmy Button had a great horror of these men, under the name of “Ohens men”. “When the leaf is red, he used to say, Ohens men come over the hill & fight very much.”