Zane Grey 
Ken Ward in the Jungle [EPUB ebook] 

Excerpt: ""What a change from the Arizona desert!" The words broke from the lips of Ken Ward as he leaned from the window of the train which was bearing his brother and himself over the plateau to Tampico in Tamaulipas, the southeastern state of Mexico. He had caught sight of a river leaping out between heavily wooded slopes and plunging down in the most beautiful waterfall he had ever seen. "Look, Hal, " he cried. The first fall was a long white streak, ending in a dark pool; below came cascade after cascade, fall after fall, some wide, others narrow, and all white and green against the yellow rock. Then the train curved round a spur of the mountain, descended to a level, to be lost in a luxuriance of jungle growth. It was indeed a change for Ken Ward, young forester, pitcher of the varsity nine at school, and hunter of lions in the Arizona canons. Here he was entering the jungle of the tropics. The rifles and the camp outfit on the seat beside his brother Hal and himself spoke of coming adventures. Before them lay an unknown wilderness–the semi-tropical jungle. And the future was to show that the mystery of the jungle was stranger even than their imaginings."