of Zmimac. or Yangoma. 6? 
The distances, denoted ,l)j Roman numerals in the second 
map, are days’ journeys ; those denoted by cyphers are leagues 
of Ava. Both in the maps and account I have used the con- 
traction M. for Mam or Hmain^ the Siammese name for a 
city. 
Art. ^.-—Observations on M. Beudanfs Opinions regard- 
ing the Crystalline RocJcs qf‘ the Red Sandstone Formation^ 
as expressed in the Sd volume of his “ Voyage en Hongrief 
from p. 194. to p. 206. By Aime' Boue',. M. D.- Member 
■ of the Wernerian Society, &c. 
It is a well known axiom, that nothing contributes more to 
the advancement of science than controversy ; and, for this rea- 
son, I have thought it proper to offer you some reflections upon 
M. Beudanfs ideas regarding the origin of the crystalline depo- 
sits which are included in the oldest secondary formations. 
These observations will appear to you the more necessary, that 
they are written with the view of contradicting the opinions of 
a geologist, who seems anxious to evince great theoretical impar- 
tiality, and who, on this account, inspires a great degree of con- 
fidence in the minds of his readers. Besides, were I to pass 
over his remarks in silence, it might seem as if I began to feel 
that my opinions were no longer tenable ; whereas, in fact, I am 
every day receiving additional proofs of their accuracy. 
This theoretical controversy is by no means unconnected with 
the progress of true geological knowledge, as is the case with too 
many others, for the adoption of Neptunian or volcanic ideas 
necessarily leads to different geognostical results : with the for- 
mer the geologist cannot acquire a true idea of the singular po- 
sition of the crystalline secondary deposits ; he is exposed to nu- 
merous errors ; he is astonished to find crystallised masses 
amongst arenaceous ones, and at last is obliged to suppose me- 
chanical deposits alternating with chemical ones, of which our 
present degree of chemical knowledge does not shew us the phy- 
sical possibility. 
Before opposing my arguments to those of M. Beudant, and 
before proceeding to demonstrate that tlie origin of the crystal- 
E 2 
