In this, the first attempt to give in English a comprehensive review of petrographic methods, it cannot be otherwise than that there should be many omissions—it is to be hoped not many errors. If any is found the author will be extremely glad to have his attention called to it, as he will also be for criticisms, or suggestions for additional material that should be included.

This AWWA revision to Manual M21 is the culmination of nearly three years of effort by members of the Groundwater Resources Committee. This edition has been written to provide the reader with a general understanding of the principles involved with ground
water, its movement and character, and the subsequent impact these characteristics have on the design, construction, and maintenance of groundwater well systems for water utilities.

In geological maps, the undulation of the topography is represented by height contours. These contours represent lines along which all the points have the same altitude. Height contours are represented usually by broken lines and the numbers attached to them indicate the altitude of the corresponding contour.

Landsat Thematic Mapper [TM) data have been used to detect the presence of altered rocks associated with ore mineral deposition. In arid environments, the spectral signatures of diagnostic minerals are often not masked by water, vegetation, or suxficial materials. There are many studies in which TM data have been used to locate hydrothermally altered rocks in near desert regions, but few successful examples can be found that relate to glaciated, vegetated terrain at high latitudes. In this paper, TM data, in concert with lithogeochemical data and field observations, are used to detect and map altered rocks in the Sulphurets-Brucejack Lake district of northwestern British Columbia.