CONSTITUTION AND ORIGIN OF SPHERULITES. 417 
In the “Tableaux des Mineraux des Roches” by Michel- 
Levy and Lacroix, issued in 1889, p6trosilex is mentioned 
under quartz, and summarily defined as a “ melange de 
quartz spherolitique dominant et de feldspath.” Its chemical 
composition is given as “Si 0 2 + un pen d’alumine et 
d’alkalis; ” its characteristic form as “ Spherolites & fibres 
surtout positives,” and its color is said to be “ brunatre.” 
This definition is precise, but it by no means covers the 
usages to which the term is put in petrographical literature, 
and is directly opposed to many statements of the properties 
of the substance—as, for example, the one above cited. One 
of the results of the present investigation seems to explain 
in a measure the confusion of properties attributed to petro- 
silex, as will appear later on. 
Michel-Levy divides spherulites into five groups, which 
he designates as follows: 1st, “ Etoilements des micro¬ 
pegmatites ; ” 2d, “ Spherolites a quartz globulaire; ” 3d, 
Spherolites petrosiliceux a croix noire; ” 4th, “ Spherolites 
d’orthose;” 5th, the spheres of perlite. The last group is 
excluded from present consideration, the second includes 
peculiar and usually secondary forms of a single rock con¬ 
stituent of minor importance. The fourth group is said 
to represent the “ Sphserokrystalle ” of Rosenbusch. The 
classification of Michel-Levy has no place for spherulites 
composed of known minerals, unless they be quartz and 
feldspar intergrown in the manner of micropegmatite. His 
third group corresponds to the felsospherulites of Rosenbusch, 
and as a matter of fact the great majority of spherulites are 
referred to this division, petrosilex, like microfelsite, being 
readily assumed to be present where the spherulite is very 
dense, or when it is clouded by decomposition products, or 
when the sections are too thick for microscopical analysis. 
It is to be noted that the French author does not recog¬ 
nize among spherulitic bodies of rocks any representatives of 
Vogelsang’s cumulites and globospherulites; at least he does 
not provide for them in his classification. 
Existing literature concerning spherulites is almost exclu- 
