ELtSHA MITCHELL SCIENTIFIC SOCIETY. 109 



great stiiiiiilus to nie in seeking to increase to the utmost the accnracv of niv 

 portion of the labor. The manner of preparing the manuscript maps, l)y 

 noting the points where diflerent rocks pi-esent themselves, and afterwards 

 connecting such points in accordance with nature, is too readily coniprehended 

 to demand fartiier esplanation. 



But there are instances where tiie maps might possibly engender the belief, 

 that an amount of accuracy had l>een attained which would, under no circum- 

 stances, be within tlie reach of an examination of the surface. Where solid 

 rocks are observed out-cropping ncMr the margin of their area, the case is easy 

 of solutic^n ; nor is the difficulty of the determination of boundaries much 

 increased, where a conspicuous variation in the soil is seen, and the mother- 

 rock of such soil is known; but many soils, derived from distinct rocks, are 

 very similar in character (those of granite rooks and mica-slate, for instance), 

 while some again, from their lightness, are drifted into the area of another 

 rock. In these instances we are forced to rest satisfied with the utmost aitain- 

 Kible accuracy. But as a uniform rule, precision in all details has been aimed 

 at. Hence, the region around Limestone Springs, whose great scientific and 

 t-echnological interest ap[)eared to demand the utmost care, was first drawn on 

 a scale of one statute mile to two inches. From this manuscript, the plate 

 XII was reduced by Mr. Colton. The ordinary scale on which the manu- 

 script maps are drawn is that of two miles to the inch, the subsequent reduc- 

 tion being to a scale of five miles to one inch. 



As the maps of Report I were the first regularly printed in colors in the 

 United States, it was necessary to make a number of experiments in regard to 

 the manipulation of the work, before arriving at that degree of excellence 

 which, I certainly think, Mr. Colton has now successfully attained. A great 

 difference is even observable between the maps accompanying the different 

 Reports. Those of the First were engraved on stone; those of the Second on 

 zinc, and those of the Third and Fourth on copper, without any increased 

 expense, the recent improvements in the art of engraving having rendered 

 the latter sufficiently cheap for the purpose. In comparing these maps with 

 those coloretl by hand, the incomparably greater accuracy of the printed 

 ■colors will appear at once, and it is, therefore, with gratification that we may 

 perceive our State to be the first to introduce a new system, as it were, in a 

 branch of engraving in which, until recently, almost all other countries have 

 far surpassed us. These colors are applied in such a way that the blue, for 

 instance, is era[)loyed for the blue, purj)le and green ; the yellow for the yel- 

 low, orange and green; the red for the red, purple and orange-^^so that the 

 impression of one and the same color applies to different rocks, by being used 

 alone or in combination. In the maps of the present Report (for 1859), a great 

 additional improvement will be seen in the representation of the gradual pas- 

 sage of one rock into another— a highly important feature, which it would be 

 impossible to indicate with uniformity and precision by hand-coloring. The 

 colors employed throughout have been the deep and decided ones seen in the 

 $?e()gnostic maps of continental Europe, which appeared to me far preferable 



