456 
album Greene. The paper was illustrated by 
herbarium material and by samples of the flow- 
ers of each species preserved in formalin. While 
the main characters lie in the shape of the calyx 
and corolla tube, the habit and foliage of the 
plant afford good diagnostic points. 
Mr. O. F. Cook discussed certain new or lit- 
tle known species of Amanita, commenting on 
their structure and relationships. 
The ninth regular meeting of the Club was 
held September 6, 1899, and was devoted to an 
informal account of the Alaskan flora by Mr. 
Frederick V. Coville, who was a member of the 
Harriman expedition. 
CHARLES LOUIS POLLARD, 
Secretary. 
DISCUSSION AND CORRESPONDENCE. 
ON THE DEFINITION OF GEOLOGICAL TER- 
RANES. 
SURPRISING as it may seem to those who are 
not professional geologists, it nevertheless with 
truth may be said that until within the last de- 
cade or two there existed little demand for the 
concise definition of geological terranes and for- 
mations. The mere application of a name was 
almost enough to establish it. In this connec- 
tion there was often also an enumeration of the 
common fossils contained, or a somewhat gen- 
eralized vertical section of the rock layers. 
One or the other of these features and a knowl- 
edge of the typical locality at which the rocks 
were exposed often enabled the terrane to be 
subsequently recognized and the title to be 
used. 
At the present time all is changed. With 
the systematic introduction of local geographic 
names for the geological terranes, and the gen- 
eral adoption of criteria of discrimination other 
than those afforded by fossils, there has come 
to exist an urgent need for more accurate defi- 
nition of terms. The degree of accuracy now 
demanded is comparable to that attained in 
other branches of science. The requirement is 
for definition based not on trivial or accidental 
characters, but upon features that are not only 
really determinative, but recognizable in the 
field. 
The classes of characteristics that require at- 
tention are not many, yet in the description of 
SCIENCE. 
[N. 8. Von. X. No. 248. 
geological terranes it rarely happens that any 
of these features are clearly pointed out, or 
when mention is made of them that they are 
equally compared. When a new name of a 
rock terrane is formally proposed, about the 
least thing that its author can do, if he wishes 
his term to be considered by his fellow workers, 
is to tabulate the leading characteristics and 
differences as compared with associated ter- 
ranes. 
In the past there has been little or no neces- 
sity for very exact discrimation ; hence in using 
the title suggested by the workers of a genera- 
tion or more ago we have to do the best we 
can, giving the pioneers the benefit ‘of all 
doubts. When titles are applied to terranes 
now there is cogent demand for formal enu- 
meration of essential features. 
Exactly what should constitute a proper defi- 
nition of a geological terrane may give rise to 
some differences of opinion. But there should 
be no variance of views regarding what points 
should be especially mentioned. Little or no 
attempt has yet been made to formulate these 
groups of essential characteristics. They ap- 
pear, however, to fall naturally under six cate- _ 
gories, which may be termed: (1) geographic 
distribution, (2) topographic expression, (3) 
lithologic nature, (4) stratigraphic delimitation, 
(5) biologic definition, and (6) economic con- 
tent. 
1. Geographic Distribution is of first impor- 
tance, as it fixes the terrane in space. The 
actual area occupied, or the amount of territory 
over which it forms the surface rock, is largely 
a function of the present attitude of the rocks. 
When the beds are horizontal, or nearly so, the 
surface distribution closely coincides with the 
original lateral extent. The area occupied is 
broad. As the degree of tilting increases, 
owing to orogenic movement that took place 
after the sediments were laid down, there is a 
narrowing of the zone until, when the strata 
stand vertically, it reaches a minimum breadth. 
In the definition of a geological terrane the 
matter of geological distribution is not only of 
much greater import than it was formerly 
supposed to be, but it is a factor that is con- 
stantly becoming more valuable for the reason 
that rock units are now being named after 
