382 PROCEEDINGS : BOSTON SOCIETY NATURAL HISTORY. 
that the difference between them and others is merely in their 
attitude and the character and origin of the fissures. 
If the quartz and calcite are not directly sedimentary in their 
nature, they must have one or more of three origins. They came 
from below, or from the surrounding rocks of about the same 
horizon, or from above. If thev descended, the solutions must 
have been cold, and the same probably may be said if lateral secre¬ 
tion accounts for their presence. There were no cross-fissures, else 
the water would have deposited its burden in them. If any gold 
existed in the sediments, its collection might have been effected ; 
but the concentration of gold appears to have taken place for the 
most part at a later date than that of the formation of the first 
crevices. Solutions would penetrate more readily the coarser and 
looser textured sandstones, and the finer grain of the pelites below 
would cause deposition of minerals along the contact. But we find 
veins at the under as well as the upper contacts of slate strata. If 
the clay intercepted descending solutions, the veins ought to be 
most frequent in the upper portion of the series, where there is 
abundant opportunity for such interruption. But they are by far 
the most common near the middle, where the proportion of slate 
to sandstone is greatest. 
Against lateral secretion the same arguments hold, in part. The 
coarser beds do not look as though much silica had been carried 
through them in solution, for they have comparatively little sec¬ 
ondary growth on the quartz grains. The silica necessary for the 
formation of the veins would have necessitated an extensive leach¬ 
ing of the surrounding rocks, and would have left its mark in the 
condition of those rocks; and the arenaceous sediments, which were 
■formed principally from sand, would probably have received most 
of the veins. 
It is more natural, and in better accord with the facts, to suppose 
that, although the veins lie parallel to stratification planes, they 
came from below in the same way that many others have done, and 
were formed from hot waters which bore various substances in 
solution. Their distribution appears to have no reference to a pos¬ 
sible local supply, but does agree with planes of weakness along 
which they could force their way under pressure. There is much 
calcite in the cement of the arenaceous sediments; and it might be 
supposed that at least this portion of the gangue came from them. 
But usually it is either closely mixed with the quartz or fills the 
