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POPULAR SCIENCE REVIEW. 
exploded during the second week of December at the Royal Arsenal, Wool- 
wich, it was already fully charged, and the maximum pressure had been 
applied in safety. It is the custom, it seems, however, to leave the pressure 
on the rocket for one minute after reaching the maximum, and it had been so 
left for three quarters of a minute when the explosion occurred. The usual 
conjecture that such accidents are produced by an atom of dirt, the friction 
of the tamping tools, or any such causes, are therefore untenable in this 
case, and the origin of such explosions remains unknown. In future the 
rockets are to be filled and pressed in a bomb-proof room, and the men em- 
ployed on the work are to be protected by iron shutters from any mishap. 
GEOLOGY AND PALAEONTOLOGY. 
Spirifer Icevis, fyc. — Prof. H. S. Williams communicates to Silliman's Journal 
an abstract of some researches made by him upon the Spirifer Icevis of the 
Portage group of New York, and its relations to other forms occurring in 
other groups of Palaeozoic rocks. His remarks are interesting as illustrating 
in a very remarkable manner the affiliation of so-called species in successive 
formations, detailed examples of which have rarely been so clearly put 
forward. 
The more important characters of the species are distributed by Prof. 
Williams under the following seven heads : — (1) Form and proportions of the 
shell; (2) size; (3) prominence and over-arching of the beak; (4) the short 
and high cardinal area ; (5) the triangular aperture covered by an arched 
pseudo-deltidium ; (6) the smoothness (non-plication) of the surface ; (7) the 
concentric series of minute radiating lines covering the surface. The last 
peculiarity has not previously been recorded as characteristic of the species, 
nor has it been noticed by writers on Devonian Brachiopods. 
By careful comparison of characters, Prof. Williams arrived at the result 
that a genetic relationship exists between Spirifer Icevis and S. fmbriatus, 
which occurs in the Hamilton and earlier formations. Then, tracing back 
the forms exhibiting the peculiar combination of characters which appeared 
to be essential to the two species just mentioned, he found the earliest trace 
of them in the Niagara formation at the bottom of the Upper Silurian. 
Here the central type of the primitive species is S. crispus, His., of which 
S. bicostatus, Hall, is probably an extreme variety, and S. sulcatus, His. an 
extreme variety in the other direction. Spirifer crispus, with corresponding 
varieties, is very abundant and very widely distributed, occurring at the 
horizon indicated wherever that is represented. The author also traced this 
type of Brachiopods forward to Spirifer glaber, Mart., and other Carboni- 
ferous forms. 
The following is an abridgment of Prof. Williams’ conclusions : — What- 
ever theoretical description we may give to species, we have here, in the first 
place, an abundance of organisms whose remains are found in Upper Silurian 
rocks of Europe and America, presenting a few clearly marked, distinctive 
characters variously developed in the individual forms, but so grading in the 
different varieties as to cause careful naturalists to associate them as varieties 
