Review of Recent Geological Literature. 303 
waves of gravitation, whereas if those emanations had remained 
unchanged, their numbers would be suflBcient to flood the earth with 
insufferable light and heat. 
5. We reckon the dispersion and divergence of light and heat from 
some point on the surface of the luminous body, but we reckon gravi- 
tation from the center of the mass. These resemblances and contrasts 
are all beautifully accounted for on the supposition, as required by the 
author's theory, that the undulations that produce light and heat are 
outward, from the sun, and those that produce the resultant motion we 
call gravitation an inivard toward the sun, the latter originating from 
the surrounding spheres, infinite in number and infinite in their power, 
sufficient to cope with any mass they may encounter, although start- 
ing from their sources as highly luminiferous and thermaniferous, 
perhaps, as those that issue from our sun. 
(TO BE CONTINUED.) 
Structures et Classification des Roches eruptives. Par A. Michel Levy, 
Paris, 1889. 8vo. pp. 95. 
This memoir is, in eff'ect, a detailed review of the second edition of 
Rosenbusch's Mikroskopische Physiographie der massigen Gesteine, It 
bears the impress of a master hand. American students have been 
drawn to the study of the German experts in modern petrography, 
and to a large extent, have become partisans of the German school. 
Among the Germans, Rosenbusch seems to be conceded the first place, 
and it is impossible to deny that his great work embodies a vast 
amount of compilation and original research. It will be useful how. 
ever, to bear in mind the fact that the splendid quarto volumes of MM. 
Fouque and L6vy appeared in 1879, and that tlie results which that 
work embodies began to see the light as early as 1874. The first edi- 
tion of Rosenbusch appeared from 1873 to 1877 ; but the second edition, 
which has inaugurated the revolution in petrography, dates from 1887. 
Not only is this priority of publication due to MM. Fouque and Levy, 
but the student of their writings will discover valid grounds for M. 
Levy's claims as set forth in this review, to priority of conceptions and 
of terms. 
To illustrate the case, we may introduce a few specifications : Ros- 
enbusch's distinction of rocks into holocrystaUine and hypocrystalline 
corresponds very nearly to Levy's distinction into granitoid and trachy- 
toid {or porphyric). This conception was announced by Rosenbusch 
only in his new edition, but by Levy it was announced in 1874, and 
again in 1875. The microgranulites of Fouqu^ and Levy presenting 
passages to a granitic structure, but without the habit of granites, 
have been renamed microgranites by Rosenbusch, though referred to 
his group of quartz-porphyries. The term petrosilex, as used by authors, 
is changed by Rosenbusch into microfelsite. Vogelsang had denomi- 
nated as granophyres, those quartz poryphyries with a granular magma, 
as felsophryes, those with a petrosiliceous magma, and as vitrophyres, 
those with a vitreous magma ; but Rosenbuich changes the term gran- 
ophyre from its original signification by embracing under it the three 
