174 Reviews — Poussin 8f Renard — Belyium Sf the Ardennes. 
frora the other two.” And that “the peculiar form and arrangement 
of the teeth in the first of these render necessary the institution of 
a new genus, to which I have given the name of Gonatodus.” He, 
however, preserves Agassiz’s name of punctatus for the species ; but 
redescribiug it from original and careful observation of the more 
complete material at bis command. He further observes that “the 
peculiar dentition of Gonatodus was, however, first correctly de- 
scribed by Mr. R. Walker, in a fish from the oil shales of Pitcorthie, 
Fifeshire, to which he gave the name of Amblypterus ancono- 
a;c}modus. ,, And that “ Mr. Walker’s fish undoubtedly belongs to 
the same genus, and may possibly be the same with G. punctatus .” 
Gonatodus macrolepis, Traq., is a new species, ranging in length 
from four to seven inches, and oecurs in the Blackband Ironstone. 
The configuration of the bones of the head, as far as they can be 
defined (for in the specimens examined they are all more or less 
crushed and broken), and their sculpturing, and also the configuration 
of the teeth are essentially the same as in the preceding species ; but 
the scales on the anterior portion of the body are considerably 
larger than in G. punctatus, and as in that species the surfaces are 
brilliantly polished, and devoid of ornamentation, and their posterior 
margins are finely denticulated. 
Arnple and clear as are the descriptions, we cannot conclude with- 
out expressing regret that they have not been supplemented by good 
figures of the specimens upon which the species have been fouuded. 
W. D. 
Y. — Memoire sur les Caracteres Miner alogiques et Strati- 
GRAPHIQUES DES ROCHES DITES PlUTONIENNES DE LA BeLGIQUE 
et de l’Ardenne Franqaise. By Professors C. de la Vallee 
Poussin and A. Renard. 4to. pp. 264, and 7 plates. (Brussels, 
1876.) 
D E SAUSSURE declared that mountains were not to be studied 
witli the microscope. What would that venerable fatlier of 
geology think could he see the “slicing” of rocks which is now 
going on all over Europe ! It was the custom, not so very long ago, 
for geologists to be content, for descriptive purposes, with a small 
stock of words wide and rather vague in meaning — of which “trap ” 
is a worthy example — words which bound one to very little or 
nothing. A hand-lens to be used in the field was the only auxiliary 
thought of in determining the lithological characters of rocks. Now 
all is changed, the geologist trembles as he hazards a name for the 
speciinen he collects, for he knows not how wrong he may be proved 
to be by that newly-arisen votary of Science — the Micro-petrologist. 
The rock-nomenclature of liis youth is gone, he knows nothing of, 
and finds it hard indeed to learn tlie meaning of “ fluidal structure,” 
“ devitrification,” “ globulites,” “belonites,” or “ margarites,” and 
the result is that he, as a rule, gives up the attempt, and relies, for 
the- determination of liis rock-specimens, on the knowledge of those 
who have made micro-lithology their special study. In England the 
number of these specialists is small but increasing, headed as they 
