NAUMANN ON GNEISS AND GNEISS-GRANITE. 3 
their contortions resemble those of gneiss or mica-slate. Scrope more- 
over remarks, that the layers are more frequently vertical than hori- 
zontal, and may have been caused by the protrusion of the masses, 
exactly like those of the perlites of Oyamel in Mexico, the stripes of 
which are also vertical. The author makes the following striking 
remark :—that many similar appearances, as, for example, the parallel 
structure of phonolites, and the very frequent elongations and contor- 
tions in gneiss and mica-slate, may owe their origin to similar causes. 
These observations and views of Scrope were afterwards fully con- 
firmed by Abich*. He distinctly calls the rock of which the great 
dykes in Palmarola consist, a schistose rock, the layers of which are 
often as thin as paper. 
What Scrope and Abich found in the island of Palmarola, was 
seen by Hoffmann in the small island of Basiluzzo, one of the Lipari 
group, where he found a trachyte composed of a reddish base, in- 
cluding many small crystals of glassy felspar, scales of mica, and 
quartz-like grains; these grains are however arranged in parallel 
stripes, which not only impart to the stone a perfect foliaceous tex- 
ture, but also give the rock a distinct laminar structure, and clea- 
vaget. 
The crater of elevation in the island of Pantellaria, between Sicily 
and Tunis, is composed, according to Hoffmannf, of a trachytic lava, 
which throughout has a foliated texture resembling gneiss, and occurs 
in beds that dip regularly outwards from the centre of the island. 
While so many instances were known of the existence of parallelism 
of structure, often in a most remarkable degree, in volcanic, and 
therefore unquestionably eruptive rocks, it was hardly to have been 
expected that there should have been so unconditional and so general 
an admission of the hypothesis that all parallelism of structure is a 
proof that the rock must originally have been formed by sedimentary 
deposit. 
It is moreover perfectly well known, that many erupted rocks, not 
of volcanic but of plutonic origin, have this same parallel texture and 
bedded structure. I need only refer to the cases of phonolite, the 
structure of which, especially when weathered, sometimes approaches 
very near to that of clay-slate ;—of the foliated porphyry described 
by Heim§, consisting of alternate layers of reddish clay-stone and 
quartz, so thin that the rock might appropriately be called paper- 
porphyry ;—of the similar kind of porphyry found in several parts of 
Saxony, especially in the neighbourhood of the Triebisch valley ;—of 
the porphyry of Frejus, described oy Elie de Beaumont as having a 
riband and even schistose structure||;—of the slaty porphyry of 
Deville in the Ardennes, which, from its structure, has been held to 
be an altered slate ;—of the porphyry of the Wagenberg on the Berg- 
_ * Natur u. Zusammenhang der Vulcanischen Bildungen, 1841, s. 19, 
t This is also confirmed by Abich in the same work, p. 85. 
~ Poggendorf’s Ann. Bd. 24. s.68; and Geognost. Beobacht. auf einer Reise 
durch Italien, 1839, s. 108. 
§ Geol. Beschreib. des Thiiringer Waldes, Th. ii. s. 159. 
|| Explication de la Carte géologique de la France, vol. i. p. 479. 
B 2 
