The lava sheet flowing around or over a standing or fallen tree took a perfect impression of its trunk and bark. Thousands of these old tree casts are found near both Adams and St. Helens. Where the lava reached a watercourse, it flowed down in a deeper stream, a river of liquid rock. Lava is a poor conductor of heat; hence the stream cooled more quickly on the surface than below. Soon a crust was formed, like the ice over a creek in winter. Under it the lava flowed on and out, as the flood stopped, leaving a gallery or flume. Later flows filled the great drain again and again, adding new strata to its roof, floor and sides, and lessening its bore. Long after the outflows ceased, weathering by heat and frost broke openings here and there. Many of the flumes were choked with drift. But others, in the newer lava beds, may be explored for miles. It was from the lava caves of northern California that the Modoc Indians waged their famous war in the Seventies. [Illustration: Mount Adams, from Snow-Plow Mountain, three miles southeast of the snow line; elevation 5,070 feet, overlooking the broad "park" country west of Hellroaring Canyon.] [Illustration: COPYRIGHT, S. C. SMITH Wind-whittled ice near the summit of Mount Adams.] The disintegration of the lava galleries in the Mount Adams field has of course produced caves of all sorts and sizes. Where one of these is closed at one end with debris, so that the summer air cannot circulate to displace the heavier cold remaining from winter, the cave, if it has a water supply, becomes an ice factory. The Trout Lake district has several interesting examples of such _glacieres_, as they have been named, where one may take refuge from July or August heat above ground, and, forty feet below, in a cave well protected from sun and summer breeze, find great masses of ice, with more perhaps still forming as water filters in from a surface lake or an underground spring. The Columbia River towns as far away as Portland and The Dalles formerly obtained ice from the Trout Lake caves, but at present they supply only some near-by farmers. [Illustration: Mazama glacier, at head of Hellroaring Canyon. Upper view shows floor of canyon, a mile below the glacier, with the "Ridge of Wonders" on right. Lower view is from ridge west of the canyon, near end of Mazama glacier, elevation nearly 7,000 feet. Note great lateral moraine which the glacier has built on left.]