THE AECHEAN. 177 
on the surface under only atmospheric pressure, and which hence 
contain considerable isotropic or glassy material. In each of 
these divisions the local geologist can subdivide to suit the needs 
of his particular map, by variation in the given color or tone, 
taking care to assign in general the darker shades to the more 
basic rocks, the lighter ones to the more acidic." 
Prof. Geo. H. Williams : " Yes." 
Prof. Hitchcock : " Yes." 
Prof. N. H. Winchell : " I think there is too great a simi- 
larity in the first three colors, but as they may not be generally 
needed on the same map, they may not occasion any confusion." 
Mr. Thomas Macfarlane : " I would like to see an addi- 
tional and darker color used to denote the modern basic eruptions, 
leaving the color 'eruptions actuelles' to represent modern acidic 
lavas. The other six colors might be used with a little precision 
in the following way : The color representing Granite, Syenite, 
etc., I would consider as applicable to the acidic eruptions of 
primitive and primary time ; while the Serpentine color would 
denote besides the basic eruptions, Urgriinstein, Norite, Gabbro, 
etc. Similarly, the colors for 'porphyres' and 'melaphyres' 
would represent respectively the acidic and basic eruptions of the 
Paleozoic and Mesozoic eras. Lastly, the colors of the Tra- 
chytes, Phonolites, etc., and for 'Basalts, Dolerites,' etc., would 
denote the acidic and basic eruptions respectively of Tertiary and 
pre-historic time. I here introduce a table, which is an attempt of 
mine to elaborate the one given on p. 105 of your report,* and to 
find room for as many as possible of the names of groups, systems, 
etc., which are now competing for recognition." (See next page.) 
Prof. Emerson : " Yes." 
Prof. A. Winchell: "On the whole, yes, but do not favor 
a division designated ' Serpentine.' " 
Of the above replies those of Le Conte, Williams, Hitch- 
cock, N. H. Winchell (with a minor objection not insisted on). 
Prof. Emerson and A. Winchell (one point excepted), approve 
Lossen's system. Powell, Hunt, Irving, Emmons, and Mac- 
farlane do not. Dawson, Dana, Wadsworth, and Dutton 
express no opinion. 
It is quite evident that the scheme which has been adopted by 
the map-committee for the purpose of bringing out the map of 
* On Berlin Congress referred to before. 
