56 Tlw American Geologist. Jan. 1891 
its change of position from side to side of the mesial line, also for the 
interrupted ridges on each side of the trail which would be the natural 
results of the successive strokes of a flat organ, and for the appearances 
presented when the tracks turn abruptly, or when they end abruptly as 
if the animal had suddenly risen from the bottom. 
Pie suggests that the roofed burrows, resembling the forms known un- 
der the name Phytoderma, may have been produced by a burrowing 
crustacean of Silurian times. 
Scolithus he unhesitatingly ascribes to worm-burrowing, and he gives 
evidence that goes to indicate that several genera that have been 
created (Monocraterion of Torell. Pyrophyllites, and Asterophyeus) are 
to be ascribed to the burrowing of the same animal or to its trailing 
about the openings of the tubes. 
A new genus (Sabellarites) is described by the author, and to it he 
assigns two species, viz.: S. trentonensis and phosphaticus. This 
name is given to tubes which are composed of fragments of shells, 
corals, sand, or phosphatic coprolites. >the former from one-tenth to one- 
eighth inch in diameter and three centimeters or more in length, found 
in the Black River limestone near Montreal, and the latter in the Hast- 
ings group, which he considers now as probably Huronian, or " primor- 
dial." These tubes he compares with those that are constructed by the 
modern genus Terebella which consist of grains of sand and fragments 
of shells attached to a membranous lining. This shows a remarkable 
antiquity for that method of life and protection against predatory 
aquatic enemies which is found illustrated by the fresh water sheaths 
with which our ponds and streams are supplied. 
The author draws attention to the characteristics by which true 
fucoids may be distinguished from the foregoing, and mentions Butho- 
trephis gracilis, giving also two illustrations of B. granti. 
Various combinations of animal tracks and rill-marks, and even of 
rill-marks alone, have been described as genera of fucoids. Such are 
Dendrophycus, Delessorites, Vexillum, Aristophycus, Chlocphycus. 
Tricophycus and Dictuolites. 
Experiments on the constitution of the natural sMca&es. F. W. Glakke 
4ind E. A. Schneider. (Am. Jour. Sci., Oct.. Nov.. Dec, 1890.) The 
authors have made a series of experiments on six groups of magnesia n 
silicates, viz.: olivine, talc, serpentine, chlorite, mica and vermiculite, 
n>ins in some cases samples from several localities. The test experi- 
ment, after ordinary quantitative analysis, and the purification of tlw 
material, or the determination of its inclusions, was the subjection of 
the ground mineral to dry hydrochloric acid gas at a temperature be- 
tween :>,s?>° and 412° C, I. e. between the fusing points of lead iodide 
;iikI zinc. The effect was different on different minerals. This was 
then compared with the effect of aqueous hydrochloric acid on the 
same minerals, sometimes after strong ignition. It was found that 
sometimes a species previously soluble could be thus split up into a 
soluble and an insoluble part. 
