222 
SCIENCE. 
groupings more complex than those which give 11s the yel- 
low and green lines. The visibility of the green lines, 
which are short, in the flame, taken in connection with the 
fact that they have been seen alone in a vacuum tube, is 
enough for my present purpose. 
With regard to the second 'point, the passage from the 
heat-level of the flame to that of the spark after volatiliza- 
tion is complete, produces no visible effect, indicating that 
in all probability the effects heretofore ascribed to quantity 
have been due to the presence of the molecular groupings 
of greater complexity. The more there is to dissociate, the 
more time is required to run through the series, and the better 
the first stages are seen. — Nature. J. Norman LOCKYER. 
THE RICHMOND DIATOMACEOUS EARTH. 
The stratum of fossiliferous earth underlying the cities 
of Richmond and Petersburg, in Virginia, when first dis- 
covered by Prof. Wm B. Rogers, in 1842, was supposed to 
be peculiar to those localities ; the further investigations of 
geologists have shown it to be a material constituent in 
various parts of the great Tertiary formation which bounds 
the continents of North and South America, and, perhaps, 
those of the Eastern Hemisphere also. To Mr. Charles 
Stodder we are indebted for the interesting and suggestive 
fact, that a stratum of infusorial earth, apparently ue same 
as the Richmond deposit, has been struck at a depth of five 
hundred feet at Fortress Monroe, in boring an Artesian 
well. 
The deposit at Richmond has long been famous with 
microgeologists for the great variety of beautiful forms it 
contains ; the illustrious Ehrenberg having assigned to it 
one hundred and twelve species— nearly double the num- 
ber to be found at any other place on the Atlantic coast ; 
and the subsequent researches of microscopists have shown 
it to be perhaps the richest deposit of the kind in the 
world, every new preparation of the earth revealing some 
forms not before noticed, many of the most interesting re- 
maining unnamed or described to the present day. The 
stratum varies in thickness from twenty to forty feet, and 
Major Bolton, engineer of the Church Hill tunnel, at Rich- 
mond (which runs through the deposit for three-fourths of a 
mile), informed me that at certain points of that excavation 
it reached a maximum thickness of eighty feet. In addition 
to an inexhaustible supply of the Diatomaceous earth, that 
work brought to light thousands of fossil remains of the 
gigantic marine monsters that, long ages ago, swam in the 
deep ocean over the spot where the city now stands. 
An observation of the sections made by the various 
water courses which cut through the plateau on which 
Richmond is built, shows the deposit to be nearly level — 
its upper surface about fifteen or twenty feet below the top 
of the ground, and perhaps one hundred feet above tide- 
water. The Petersburg deposit was regarded by Prof. 
Tuomey as belonging to a different geologic era from that 
at Richmond, as evinced by the fact of his finding the casts 
of Pectens and other Meiocene fossils below that deposit, 
while at Richmond they are found above. The great differ- 
ence in the character of the two deposits would also indi- 
cate this, the Petersburg Diatoms being generally much 
more transparent than the Richmond forms, and differing 
also materially in species. Upon exposure for sometime 
to the weather, this earth assumes an almost snowy white- 
ness, and crumbles to a fine powder, but as first dug from 
the depths of the earth it resembles bituminous coal in 
color and solidity — so tough and hard is it, that in remov- 
ing it from the tunnel it was blasted with gunpowder just 
as any other rock. Its composition, as nearly as can be 
estimated in a general way, is — 10 per cent, unbroken forms 
of the Diatomacae, 25 per cent, fine white sand, and the 
balance fine clay, formed, perhaps, mostly of the decom- 
posed and broken Diatoms, the whole mass interspersed 
with many sponge spicules and a few Polycistena, and so 
strongly impregnated with alum that many of the wells and 
springs in Richmond are injured by it. To the micros- 
copist this deposit is a source of unfailing interest, 
whilst the most inexperienced in such matters, upon 
being shown the wonderful forms found in it, are 
struck with surprise and delight. Had the pre-historic 
man possessed a microscope it might have been supposed | 
that the forms seen in this deposit may have suggested the 
forms of many of his appliances, as in it may be found 
models of almost all the implements used by savages, 
whether for war, the chase, or in domestic life ; witness, for 
instance, his stone hatchets, arrow and spearheads, knotted 
clubs, boomerangs, &c. ; a catalogue of such matters used 
by civilized people would embrace plates, dishes, cups, 
saucers, knives, forks, scissors, balls, tops, spectacles, 
watches, anchors, dumb-bells, cannon, coin, musical notes 
and many other articles ; the investigator being constantly 
startled by the strange resemblance which hundreus of 
these ancient natural forms bear to things in every 
day use. Certain varieties, however, predominate, and 
their distribution varies with level and locality, 
the upper portion of the stratum being com- 
paratively poor in forms, while they increase in 
number and variety as we descend to the lower levels. The 
genus Coscinodiscus seems to characterize this earth, and of 
it there are dozens of varieties varying from the (microscop- 
ically) enormous C. gigas to the minute and elegant C. 
stelliges which resembles closely a finely polished opal, 
requiring a lens of wide aperture and considerable power 
to show its areolations. Orthosira marina is everywhere 
abundant, whilst many beautiful forms of Navicula are 
found in every gathering. Amongst these we may specially 
note two kinds of Plcurosigma, one of which, P. 
angulatum, is a favorite test Diatom, and the other, 
which it is is proposed to call P. Virginica, (as it is 
the most common form of Pleurosigma in the Virginia 
earths), is remarkable for the beauty of its contour, which 
exactly copies a willow leaf, and the want of uniformity in 
its strise, which are much coarser in the middle than at the 
ends of the valves, It can be easily resolved with a good 
in. Objective, without the aid of oblique light. The 
genus Triceratium, is also well represented by many beau- 
tiful varieties, the handsomest of which is, perhaps, T. 
Maylandica, which can be resolved with almost the same 
ease as P. Virginica, Isthmia enervis, Biddulphia Tuomeyii, 
Terpsinae musica, Anlacodiscus crux, Navicula lyra, 
Gonphonema, Heliopelta, Asterolampra Concinna, Aste- 
romphalus, Brookeii, and Synedra, are more rarely met 
with. 
From the great variety in the markings on these valves, a 
slide of the earth, properly prepared, becomes one of the 
best and most interesting tests for the performance of ob- 
jectives, from the lowest to the highest powers in general 
use. On some of them, for instance, the areolations may 
be seen with a simple triplet, whilst on others a first-class 
objective of wide angular aperture, aided by all the modern 
refinements of illumination, is needed to show them. 
Mr. C. L. Peticolas, of 635 Eighth street, Richmond, Va., 
has sent us for inspection a few of his recently mounted 
slides of the Richmond earth, prepared by a new process for 
separating the Diatoms from the extraneous matter. We 
have pleasure in stating that these slides show the leading 
characteristics of this deposit very clearly and beautifully. To 
those who are studying these forms of fossil diatomaceae, 
the slides of Mr. Peticolas will be very acceptable, and 
they should be added to the cabinet of all who possess a 
good microscope. 
A useful list of the Longicorn beetles, or wood 
borers, constituting the vast number of insets injurious 
to our forest, shade, and fruit trees, may be found in the 
October number of The American Entomologist, briefly 
arranged in the order of their most recent classification. 
There are two beetles in the United States, both 
commonly called ‘'Fire-flies,” which are now known to 
be luminous in their larval as well as in their perfect 
state; the one Photnrus Pensylvanica, De Geer, the other 
species Photnrus pyralis, Linn. Both the males and 
females of these species have wings, and therein they 
differ from the true Glow Worm of England {La?npyns 
noctiluca), the female of which is wingless and emits a 
much more brilliant light than does her winged mate. — 
C. V. Riley. 
