SCIENTIFIC SUMMARY. 
83 
of a single species. There are well-marked typical characters, with great 
variability of the characters themselves. In the upper part of the Upper 
Silurian, we find the same typical characters, with a greater predominance 
of one or other of the variations; hut yet, in the Corniferous and Hamilton, 
the main type is represented with some variations strongly marked and 
apparently fixed, but still recognized as varieties simply. In the Portage we 
see, under peculiar conditions, a solitary race with greatly exaggerated size ; 
a luxuriant form, but still presenting the typical characters of the second 
varietal type. The same luxuriance of growth characterizes the Carboni- 
ferous forms ; but the earliest form, S. crispus of the Niagara, possessed all 
the characters which afterwards appeared in the later representatives. Thus 
the whole may constitute a physiological species ; but by intercrossing and by 
local conditions modifying the offspring, well-defined groups are produced, 
which would be called races if we knew their history, but which are called 
species because they appear at such widely separated geological periods. 
These separate groups, however, develope no neiv characters ; and there is 
every evidence for the belief that the species has lived through this long 
geological time without losing its character, and that all that has resulted 
from great time and change of conditions has been the fixing into race-groups 
of the original variable characters of the species. The species, at its first 
appearance in the Silurian, presented a decidedly new combination of cha- 
racters for the genus, and also much variation. When once these specific, 
though variable, forms appeared, they lived till the variations which could 
be played on them were exhausted ; and the species ceased to live and be- 
came extinct, either near the close of the Carboniferous, or not till later 
in the Mesozoic. Prof. Williams gives the following table of the distribu- 
tion of the forms above referred to in the American Silurian, and Devonian 
rocks 
Chemung 
Portage 
Hamilton 
Corniferous 
Oriskany 
prsematurus 
. . . laevis 
Lower 
Helderberg 
Niagara 
. tribulis . 
Saffordi (pars) 
fimbriatus . 
fimbriatus . 
subumbona 
octocostatus . modestus 
cyclopterus (pars) . 
. . Vanuxemi 
sulcatus (pars) . crispus 
crispus . 
bicostatus 
N.Y.&Tenn. 
Maryland 
New York 
^ New York 
^ Shale 
) Limestone 
— ( Amer . Journ. of Science, December, 1880.) 
Grits and Sandstones . — Mr. John Arthur 
Geological Society, on the 15th December, a 
paper on the structural characters of grits and sandstones. He described the 
microscopic and chemical structure of a large series of grits, sandstones, and, 
in some cases, quartzites, of various geological ages, noticing finally several 
sands of more or less recent date. The cementing material in the harder 
varieties is commonly, to a large extent, siliceous. The grains vary con- 
siderably in form and in the nature of their enclosures, cavities of various 
kinds and minute crystals of schorl or rutile not being rare. Mr. Phillips 
Phillips brought before the 
very interesting and valuable 
