TRANSACTIONS OF THE SECTIONS. 
585 
to the collection and arrangement of vein-stones , and to an ac¬ 
curate examination of their connexion with the rocks in which 
they occur . Mr. Taylor pointed out the importance of these 
investigations, both in respect to geological theory and econo¬ 
mical utility: he stated, that by attention to such circumstances, 
a rich vein of ore had been re-discovered at Vita Grande Za- 
rateras, in Mexico; he mentioned, also, the occurrence of a vein 
at Rumos, in the same country, under a covering of basalt.— 
Mr. Greenough adverted to analogous instances which had 
been observed in this country; and remarked that in Derby¬ 
shire the veins are often interrupted by trap, and that, at the 
point of contact, the vein sometimes separates into branches.— 
Professor Sedgwick said, that in some instances in Derbyshire, 
the veins are traced through the trap rocks; in some they are 
cut off by these rocks; but in others the veins have unquestion¬ 
ably been formed since the formation of the trap. Certain gra¬ 
nite veins, he thought, had been caused by injection under 
great pressure, and were simply a prolongation of unstratified 
into stratified masses; but the cause of granitic, and of metalli¬ 
ferous veins, did not appear to him to have been the same; the 
latter were often mere cracks, traversing the granite veins, as 
well as other rocks. In Cornwall the contemporaneous veins 
might more aptly be termed veins of segregation. So that there 
are three different sets of veins. 1st, Those of injection;— 
2nd, Those of segregation ; which comprehend several of the 
metalliferous veins of Cornwall in actual work. 3rd, Those 
which have been plainly mere fissures or cracks, and which 
have been subsequently filled—for example, by spar, ore, rolled 
pebbles, &c. No good general view of veins can be given, with¬ 
out much observation of the phenomena bearing upon this sub¬ 
ject, which are exhibited by secondary rocks. In these there 
could be no doubt of certain veins having been produced by 
fissures ; and any theory, therefore, which should assume all 
veins to be contemporaneous with the rocks inclosing them, 
must be erroneous. Cleavages, such as had been described 
as occurring in the rocks of Cornwall, were not incompatible 
with stratification: in Cumberland, and in Wales, fissile tex¬ 
ture is marked by chlorite and mica, running with parallelism ; 
beds occur also there, containing shells, which mark the real 
stratification, whilst the same beds of shells have, in many 
cases, vertical cleavages, traversed by the lines of slaty cleavage; 
and it might be inferred by analogical reasoning, notwithstand¬ 
ing the absence of organic remains, that Cornwall, also, is a 
stratified country.—Dr. Boase stated his opinion, that the slate 
rocks of Cornwall are in their original position, and have not 
