CARTOGRAPHY 187 
enlarged by making a copy to the size desired. Outline maps of 
topography may be traced from the resulting negative, and the formations 
filled in by means of the proper colors. The most satisfactory method, 
however, is to have the original views or the copy printed “light” and to 
color the formations just as they appear there, with all the wealth of topo- 
graphic and vegetational detail. If a detailed topographic map alone is 
desired, this is traced directly from the large copy. 
234. Continental maps. A method of determining the general out- 
lines of regions, provinces, and vegetational zones as a preliminary to their 
detailed study has been used successfully for several years... This is based 
upon provincial and continental maps on: which are traced the geographical 
areas of the species of genera typical of the various formations. Detail 
topographic maps of the prairie province and the North American continent 
have been used for this purpose. A number of the facies of extensive and 
representative formations of the different portions of the continent are 
selected and grouped according to genera. One map is devoted to each 
genus, unless the number of species is large. In this case a number of maps 
are used, since the limits are apt.to become confused. The range of each 
species is determined from all the reliable sources, and a corresponding line 
is drawn upon the map to delimit its geographical area. The limits of the 
area of each species are drawn in a different color, and the name of the species 
printed in the same color in the legend. Although this work has as yet been 
done only for the trees of North America, and for the grasses and principal 
species of the prairie province, it promises to constitute a final method for the 
limitation of vegetational divisions. It is clear that if the original data 
concerning ranges are accurate, the increasing study of formations will do 
little more than rectify the detailed course of the limiting line, since in most 
cases facies and formations coincide in distribution: The limiting line or 
ecotone of a zone or province is a composite obtained from the limits of: 
certain representative facies and principal species, and checked by the limits 
of species typical of the contiguous vegetations. Thus, the boreal-subalpine 
zone is clearly outlined by combining the limits of Populus tremuloides, 
Larix americana, Pinus banksiana, Abies balsamea, Picea mariana, Picea 
canadensis, and Betula papyracea, and checking the results by the areal limits 
of the hardwoods and grasses to the southward. 
?Pound and Clements. The Vegetation Regions of the Prairie Province. Bot. 
Gaz., 25:381. 1898. 
