Boston Meeting of the Geological Society. 139 
abstracting material below and adding it to the crust. Their escape 
would also accelerate the cooling of the earth, thus affecting its ther- 
mal gradient and the estimates of its age. 
7. Certain climatic features of Maryland. William B. Clark, 
Baltimore, Md. A series of large climatic charts, recently prepared for 
the Maryland State Weather Service, was exhibited, and the effect of 
the mountainous area in western Maryland and of Chesapeake bay 
upon the temperature and rainfall were explained. 
8. Dual nomenclature in geologic classification. H. S.Williams, New 
Haven, Conn. Dual designations of geologic formations were recom- 
mended, one set of names having reference to the lithological character 
of the rock-masses and being derived from geographic localities or dis- 
tricts, and the other based on the great and persistent life characters of 
the fossil faunas and floras of the rocks. The former set of names will 
be liable to vary as the strata change from place to place, or even a 
name of lithological significance will have a wide extension when the 
same conditions of deposition reached far in space or time. The latter 
names, of biological significance, will be substantially constant over 
large areas and perhaps over the world. This principle was stated by 
the author several years ago before the International Congress of Ge- 
ologists. (Report of the American Committee at the session in London 
1888, p. A91 ; also Am. Geologist, vol. ii, pp. 195, 196, Sept., 1888.) 
This paper urged the importance of recognizing in nomenclature that 
duality which is already clearly recognized in the nature of the facts 
classified. The use of Era, period, epoch, age, as simply chronologic 
names, and for the correlative structural divisions Group, system, series 
stage, is good so far as it goes; it emphasizes the distinction between 
the geological formations and the divisions of geological time. But it 
should be carried to its logical conclusion, and different names should 
be given to things which are different. The author proposes that the 
present nomenclature, which has been constructed from the outset to 
designate formations, should be restricted to that use, but should be 
applied with strict regard to the facts in each case ; the same name 
should be applied only where the same rock formation is actually rec- 
ognized ; and attention should be given to composition, structure and 
locality, in the definition of the formation. In naming the divisions of 
the time scale the method and kind of nomenclature already in partial 
use should be systematized and applied, also with precision, according 
to knowledge. The longer divisions. Paleozoic, Mesozoic, Cenozoic, are 
the Times of the geological scale. These are subdivided into arbitrary 
divisions; the systems, which were originally aggregations of rock forma- 
tions, and have come to be used as pure time-divisions which are indi- 
cated by the fossil contents. If. then, we speak of the Paleozoic time in 
a tectural sense, it is made up of the five eras named Cambrian, Ordo- 
vician, Silurian, Devonian and Carboniferous. Still finer divisions have 
been determined in each of the eras. In the Cambrian era there are 
three recognized periods, which may be called Eocambnan, or the early 
Cambrian: Mesocambrian, or the middle Cambrian ; and Neocambrian, or 
the later Cambrian. The periods are thoroughly understood by geolo- 
gists throughout the world and are distinguished by their fossils, 
characteristic genera of trilobites, as defined by Walcott. This system 
of nomenclature is easily applied to the subdivisions of each of the eras. 
It is doubtful if the knowledge of paleontology is sufficiently minute to 
define with precision any universal subdivisions of these periods. Lo- 
cally epochs and hemeras may be recognized in the life-periods of the 
species and varieties of the fossils. But in most cases the species which 
are of wide enouerh distribution to serve as means of definition of the 
time relations of the fossil faunas have a range geologically through at 
least one period. Therefore the refinement of the time scale beyond the 
period awaits the further investigations of paleontologists. 
