60 REPORT—1849. 
«« How many times, in describing my species, do I think of your assertion, which 
the facts have so gloriously justified, ‘that the Silurian system is the great centre 
of the creation of trilobites’! At that early epoch Bohemia seems indeed to have 
had the privilege of uniting an immense variety and multitude of these crustaceans ; 
for the number of my species already exceeds 200. If you think this account of the 
metamorphosis of a trilobite of sufficient importance, announce it in any form you 
please to the British Association for the Advancement of Science. 
«J. BARRANDE.” 
On the Distribution of Gold Ore in the Crust and on the Surface of the Earth. 
By Sir Rovericx Impzry Murcuison, G.C.S., F.R.S. &c. 
The recent discovery of considerable quantities of gold ore in California having 
excited the public mind, and led to some conclusions which he esteemed to be exagge- 
rated, the author took this occasion of the meeting of the British Association to bring 
forward the whole subject of the distribution of gold ore over the surface of the 
‘earth, not merely to develope his own views and those of others, but also to elicit by 
discussion, the knowledge of the assembled geologists, mineralogists, miners and statists. 
An enlarged Mercator’s projection of the world was exhibited, on which all the leading 
ridges which had afforded gold ore in times past or present, were marked, as taken in a 
great part from a general sketch-map by M. Adolphe Erman of Berlin, the explorer 
of Siberia and Kamschatka, which is appended to a geographical and mineralogical 
description of California by M. Hoppe and himself, as inserted in the ‘ Archiv fiir 
Wissenschaftliche Kunde von Russland’ (7 band, 4 heft). 
Referring to the works of Humboldt and Rose on the Ural Mountains, as well as to 
those of Helmersen and Hoffman, the former of whom constructed some time since a 
map of all the gold tracts of Siberia, and also citing the other contributions of M. 
Adolphe Erman on this head, Sir Roderick gave a condensed view of his own obser- 
vations on the gold regions of the Ural Mountains. His exploration of that chain, in 
company with his associates M. de Verneuil and Count Keyserling, led him to form 
the opinion, that great and rich gold veins had alone been produced in the oldest 
formations, and chiefly where they have been highly metamorphosed by the intrusion 
of igneous rocks; in other words, that wherever clay-slates, old limestones, and 
greywacke sandstones (whether azoic or of Silurian, Devonian and Carboniferous age), 
had been penetrated by greenstone, porphyry, syenite, granite or serpentine, and were 
consequently in a more or less metamorphic or crystalline condition, there auriferous 
quartzose veinstones most occur, containing gold ore diffused in grains, leaves, lumps, 
and irregular filaments. Every discovery in the auriferous regions of Siberia and 
’ America, as well as all the workings in the Old World in past times, confirm this view, 
and prove it to be a geological constant, that the azoic and palzozoic rocks, when 
metamorphosed, are the only great repositories of gold ore. The minute quantities 
of auriferous pyrites and gold which have been detected in the secondary and 
younger deposits do not interfere with this generalization. 
To the general view of Baron von Humboldt, that the richest gold deposits are those 
which are derived from ridges having a meridian direction, M. Adolphe Erman is de- 
cidedly opposed; but Sir Roderick is of opinion, that a much greater quantity of gold 
ore has been obtained from chains having a nearer relation to N. and S. than from 
those approaching to equatorial or E. and W. directions, due perhaps to the general 
form of the chief masses of land and the prevailing strike of the palzozoic rocks. He 
next pointed out an error into which some persons had fallen, of supposing that the 
chief Uralian mines were worked underground ; the only small subterranean work being 
one near Ekaterinburg, which affords a very slight profit. All the rich mines along that 
meridian chain, throughout 8° of N. latitude, are simply diggings and washings which 
are made in the detritus or shingle accumulated on the slopes of the ridges and in the 
adjacent valleys, and with one small exception are all upon the eastern or Siberian side. 
This phenomenon in the Ural Mountains is a necessary result of their structure ; the 
older and more crystalline formations through which the eruptive rocks have risen 
constituting chiefly the crest and eastern slopes of the chain, whilst the western slopes 
are occupied by deposits of younger or Permian age, As the conglomerates and de- 

