CARTOGRAPHY iS/ 



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 tremuloidcs, 

 Larix americana, Pinus hanksiana, Abies balsaniea, Picea mariana, Picea 

 canadensis, and Betula papyracca, 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. 



