302 

condemnation is hinted of collegiate education for our 
Indian engineers. Engineering degrees meet neither 
fayour nor contempt ; the gods of the profession seem to 
live far removed from all this turmoil, and do not deign 
even to nod approval. 
Seriously, it seems impossible that the Council of the 
Institution can rest satisfied with such a contribution to 
the cause of education as this barren pamphlet. It is 
their duty to take action ; their recommendations would 
have no legal force, but great moral weight. Let them 
say whether they desire great Polytechnic Schools on the 
continental model. Not improbably public money will 
ere long be granted for some such. Let them approve 
or condemn the Indian College. Let them recommend 
engineers to compel the attendance of their pupils at 
suitable classes, and to refuse all students as apprentices 
who cannot show that they have received proper pre- 
liminary training. If proper classes do not now exist for the 
students, let them tell us where they are wanted and what 
they ought to be. Let them declare what the preliminary 
training of a pupil must be. Let them fix a practical 
value on the engineering degrees of those colleges which 
deserve such encouragement ; or finally, if they will do 
none of these things, let them say, if they dare, that they 
are perfectly well satisfied with things as they are. 


RECENT PETROGRAPHICAL LITERATURE 
Il, 
Untersuchungen iiber die MikroskopischeZ usammensetzung 
und Structur der Basalt-Gesteine. Von Dr. F. Zirkel. 
(Bonn, 1870.) 
Mikromineralogische Mitthetlungen. Von Dr. F. Zirkel. 
Pp. 801. (Neues Jahrbuch fiir Mineralogie, 1870.) 
Reitrige zur Petrographie der plutonischen Gesteine, Von 
Justus Roth. (Reprinted fromthe Transactions of the 
Royal Academy of Sciences of Berlin.) 
Sur les Crystallites, études crystallogeniques. 
Vogelsang. (Archives Néerlandaises, 1870.) 
Kritische Mikroskopisch-mineralogische Studien. Von H. 
Fischer. (Freiburg.) 
Mikroskopische Unterschetdung der Mineralien aus der 
Augit, Amphibole und Biotit-gruppe. Von G. Tscher- 
mak. (Proceedings of the Vienna Academy of Sciences, 
1869.) 
es the Continental petrographers who have led 
the way in the recent reform and extension of this 
branch of science, none can claima more prominent place 
than Dr. Zirkel. Although still a young man, he has held 
professorships successively at Lemberg and at Kiel, and 
we rejoice to hear from him that he has been selected to 
succeed the venerable Dr. Naumann at Leipzig. He is 
the author of many excellent mineralogical and petro- 
graphical papers, and of the best text-book of petrography 
which has yet been published. Especially has he dis- 
tinguished himself by the zeal with which he has followed 
out the ideas first broadly sketched by Mr. Sorby, and 
has shown how absolutely indispensable is the application 
of the microscope to the study of the composition and 
history of rocks. His researches, while extending over 
the length and breadth of Germany, have not been con- 
fined to the Continent, but have been carried with cha- 
lepine ele 
NATURE 

[Fed, 16, 1871 



racteristic enthusiasm even as far as the peaks of Arran, 
and the cliffs and glens of our north-western isles. 
A few years ago he resolved to devote himself to a 
comprehensive study of the rocks to which the general 
name of basalt has been given. Though abundant 
chemical analyses had made the ultimate chemical con- 
stitution of these rocks well known, the mineralogical 
composition of them still remained rather vaguely defined. 
Their compactness and dark opaque hue made it difficult 
to investigate the separate mineral ingredients of which 
they consisted, and men were still speculating about the 
mineralogical nature of that part of basalt which is 
soluble in acid, when Dr. Zirkel set to work to collect 
specimens of basalt from every available locality, and to 
prepare thin transparent sections of them for examination 
with transmitted light under the microscope. The result 
of these investigations appears in the little volume now 
before us, which is appropriately dedicated to Mr. Sorby. 
In a brief introduction the author recounts the state of 
the question when he took it up. Having collected and 
prepared upwards of 300 sections of basalt from the most 
varied localities, he believes that he has obtained samples 
of at least the chief types of composition and structure 
among the basalts, and he now gives us this first instal- 
ment of his labour. 
The first section of the volume treats of the microscopic 
structure and peculiarities of the minerals which enter as 
chief ingredients into the composition of basalt—augite, 
felspar, nepheline, leucite, olivine, magnetic iron, &c. 
This is an especially valuable part of the book, seeing 
that it furnishes materials for speculating both upon the 
conditions under which basalt was erupted, and on the 
various metamorphic changes which the rock as a whole 
and its component minerals in particular, undergo under 
the influence of percolating water and atmospheric 
weathering. 
The second part deals with the general microscopic 
structure of basalt-rocks. The common notion regarding 
that structure has hitherto been that down to its 
minutest particles basalt is a crystalline rock, that its 
individual microscopic ingredients mutually impinge on 
each other, and that the difference between the structure, 
for example, of granite and basalt consists in little more 
than in the varying relative size of their component 
minerals. Prof. Zirkel, however, shows that this notion, 
which has been founded on mere deduction and not on 
direct observation, must be changed. He finds that 
in the majority of the specimens examined by him, there 
exists between the most minute ingredients a more or less 
abundant substance, not individualised into crystals, but 
amorphous, acting like a cement, sometimes glassy in 
character, sometimes half-glassy, owing to the appearance 
of hair-like particles, and sometimes completely dentrified 
so as to present a confused aggregate of darker or lighter 
minute granules, needles, hair, and crystals. He regards 
it as hardly possible to doubt that this glassy base in 
basalt is the residuum of the original »agma out of which 
the recognisable minerals in the rock crystallised, and 
that it furnishes us with a new proof of the igneous origin 
of basalt. 
In the next section the author proceeds to offer a new 
subdivision, and detailed descriptions of the basalts. He 
bases his classification upon the mineralogical composition 
a 
