region was first studied by the prolific surveyor and geologist Dr. George Mercer Dawson in 1890. Topographical maps were first produced by A.O. Wheeler in the early 1900s, and in the 1970s, Wheeler's grandson, Dr. John Wheeler, conducted an extensive geological survey from land and air. From Rogers Pass, layers of quartzite and slate are visible, revealing the fact that the range was part of a large, silty continental shelf 600 million years ago. 185 million years ago, successive plate movements from the west began to crumple and compress this material, driving some of it deep underground, and some into the heights of the Selkirks. Lime from coral and other organic life was compressed into limestone, which is seen in the Cougar Brook area. Veins of marble are present in the metamorphic rock of the high peaks. Although erosion and the effects of the glaciers are constantly grinding down the mountain peaks, the pressure of the underlying rock continues to drive them upward. Geologists have classed the rocks of the Columbia Mountains into groups, several of which appear in the northern Selkirks. The slates are in the Horsethief Creek and Lardeau groups, quartzite is in the Hamill group, limestone is part of the Badshot Formation, while the metamorphic rocks are classed in the Shuswap Metamorphic Complex. Caves The limestone strata in the park is subject to water erosion by Cougar Brook, a process that has formed the Nakimu Caves. First discovered in 1907, and originally named the Caves of Cheops, then Deutchmann Caves, this long cave system is one of the largest in Canada. The limestone is broken down and softened by carbonic acid in the brook's water. The water also contains pulverised rock from glacial processes, which serve to further etch and cut new passages in the rock. The caves contain a large concentration of a rare substance known as moonmilk - this is a suspension of calcium carbonate kept intact by bacteria. Due to its sensitive nature, and damage done to cave environments by early tourists, Parks Canada has closed the caves to the general public. Access by organized groups and experienced speleologists is allowed with a permit. Ecology Glacier National Park covers a range of habitats, from lush temperate rainforest in the western valleys, to inhospitable ice- and rock-covered alpine areas, to drier fir and pine forests on the eastern boundary. Four of British Columbia's biogeoclimatic zones