Edward Sylvester Ellis 
Boy Miners, or, The Enchanted Island, A Tale Of the Yellowstone Country [EPUB ebook] 

Excerpt: "Young Edwin Inwood leaped down from the small tree in which he had been perched for the last half hour, and ran swiftly toward the brook where his elder brother, George, and a large negro named Jim Tubbs, were waiting, ever and anon raising their heads, and looking towards the boy who was acting as sentinel, several hundred yards away, as if they were expecting some such an alarm as this. "Quick! they’ll soon be here!" he added in his terrible excitement. "How many are there?" inquired George, catching up his shovel at the same time with his rifle. "I shouldn’t wonder if there were twenty. I’m sure I saw a dozen, any way.""