...impenetrable, impenetrable... 
Gustavo Adolfo Becquer 「Legends, Tales and Poems」
... Just beyond the doorway hefound the passage completely clogged and choked by impenetrable massesof shattered rock...
Edgar Rice Burroughs 「Tarzan and the Jewels of Opar」
... She could seethe grass about her and the boles of the trees which stood out inbrilliant relief against the solid background of impenetrable night,and beyond the firelight there was nothing...
Edgar Rice Burroughs 「Tarzan the Untamed」
... For miles Livingstone and his party had to cut their way with their axes through the dense and almost impenetrable jungles which lined the river's banks...
Henry M. Stanley 「How I Found Livingstone」
...There was no guide, and the country was now overgrown with impenetrable grass and tangled vegetation eight feet high...
Samuel White Baker 「In the Heart of Africa」
...The timber grew on hillsides, and was very lofty and impressive; and the tropical undergrowth grew tall, rank, and impenetrable...
Stewart Edward White 「African Camp Fires」
...Your rowboat is runashore on a white shelving beach, and you face an impenetrable massof white walls...
Richard Harding Davis 「The Congo and Coasts of Africa」
...He had knowledge of a place where the undergrowth and bushes were almost impenetrable...
William Still 「The Underground Railroad」
...
The Impenetrable Forests...
William T. Hornaday 「Our Vanishing Wild Life」
...Layard states that the mountainbabbler frequents low, scraggy, impenetrable brush, along themargins of deserted cheena land...
J. Emerson Tennent 「Sketches of the Natural History of Ceylon」
...In the swamps of the South they make their home in dense and almost impenetrable thickets and canebrakes, where they make a nest of sticks, grass, moss and leaves...
Elmer Harry Kreps 「Science of Trapping」
...I had not gone fifteen minutes before I hadtraversed the forest, and entered the thick andalmost impenetrable bush beyond it...
Various 「Hunting in Many Lands」
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