Review of Recent Geological Literature. 181 
The interesting feature of the rock is the ground mass, which is ex 
•ceedingly fine grained and exhibits microscopically a considerable diver 
ity of structure: (1) It may be a microcrystalline granular aggregate of 
quartz and feldspar, with a preponderance of the quartz. (2) It may ex- 
hibit a structure to which the author gives no name, but which seems 
■closely similar to the micropoikilitic structure so common in ancient 
rhyolites and quartz-porphyries. (3) It may be microfelsitic. (4) It may 
be composed largely of brightly polarizing blades of a light greenish to 
colorless mica, probably sericite. (5) There occurs a more coarsely gran- 
ular groundmass, in which muscovite and biotite, which may be pri- 
mary, are abundantly present. 
Among the secondary constituents, epidote is the most abundant and 
the most interesting in its varieties. Two species are present, pistazite 
;and withamite. The latter species closely resembles piedmontite in its 
colors. The author calls it withamite only because of the scanty 
amount of manganese shown to be present by the chemical analyses of 
the rock. Similarly the occurrence of epidote and of piedmontite in 
marked abundance is a feature of the South Mountain aporhyolites. 
The eodacites show the same structures as the eorhyolites, but are 
characterized mineralogically by the presence of hornblende, while 
quartz and orthoclase become accessory constituents. 
With the pyroclastics, the author places the eutaxites (Spaltungs 
breccia) which are widespread and show many of the interesting struc- 
tures peculiar to surface lavas. The spherulitic (rarely axiolitic), the 
fluidal and the cryptopegmatitic structures are conspicuously present. 
Eovolcanics, for the most part eutaxites, are found in the region be- 
tween lakes Kolsjon and Flen and the village of Kulla, exhibiting per 
litic parting and spherulitic and lithophysal structures in great perfec- 
tion. 
The agglomerates (genuine volcanic breccias) are composed of fra<j 
ments which are not "schlierenartig," nor do they show a fluidal ar- 
rangement, but still they are not essentially unlike the main mass of the 
rock. The rhyolitic structure of Rutley and De La Vallee Poussin, the 
"Aschenstructur" of Milgge, is characteristic of a specimen from Fagge- 
mala, placed provisionally in this group of agglomerates. This structure 
Milgge,* for excellent reasons so far as the "Lenneporphyre" is con- 
cerned, considers characteristic of tuffs. Whether it is always to be so 
interpreted only continued investigation can show. In the case of the 
Smaland volcanics, and it is also true of the South Mountain volcanics, 
the absence of stratification and the transition into eutaxites argues 
against this interpretation. In this region (Sjogelo) there also occur 
some remarkable rocks, which have been characterized by Hoist as con 
glomeratic halleflintas, but which prove to be made up of spherulites 
(Kugelfels). Both the description and photograph of the spherulites 
vividly recall the spherulites of the Raccoon Creek aporhyolites. Dr. 
Nordenskjold observes that not infrequently, especially upon the weath- 
♦Unterauohungen liber die "Lenneporphyre" in Westfalen und den angrenzenden 
Gebieten; Neues Jalirbuch fur Min. Geol. und Pale., B. H. vin, 1*9:*, pp. ti»s, 649, 713. 
