VEINLETS IN THE SILURIAN AND DEVONIAN 65 
prevented the addition of new material directly through the walls, 
thus forcing it to reach the growing crystals by diffusing between the 
walls. Vugs result from a deficiency of material necessary for 
growth because of insufficient concentration or because of relative 
inaccessibility. The latter probably explains the greater abun- 
dance of vugs between chert walls. 
DESCRIPTION OF THE NON-FIBROUS VEINS 
The non-fibrous veins range up to 5 cm. or more in width and 
in some instances are exposed for distances of 15 or 20 m. along the 
strike. Where they pinch out and disappear, they are sometimes 
replaced by others a few centimeters to one side or farther along 
the line of strike. Such vein systems may be traced for over 50 m. 
The veins show no appreciable change in appearance where they 
pass from one rock to another of different texture or composition. 
A vein exposed in the limestone quarry near Farleys can be traced 
upward through the argillaceous Manlius limestone, 20cm. of 
Oriskany conglomerate, and into the Onondaga limestone, yet at 
no place is any variation in its appearance perceptible. 
The vein walls are sharply defined, and fracture usually takes 
place more readily along the contact between vein and wall rock 
than in other directions. The opposite walls of a vein are parallel 
even when they are very irregular, and they would therefore fit 
intimately together if placed in contact (see Fig. 2). Angular 
fragments of the wall rock are occasionally present in the veins; 
and in many instances, by making parallel sections, it is possible 
to prove that they are in contact neither with other fragments nor 
with the walls. Most of the fragments show no evidence of rota- 
tion although they have been displaced through distances of 2 cm. 
or more (see Fig. 3). In places a fragment adhering to both walls 
of a vein appears to have been separated into several fragments by 
continued vein growth, as in Fig. 4. 
Some veins have a banded structure with coarsely crystalline 
non-fibrous calcite in the center and a band of fibrous calcite along 
each wall. This is probably due to two stages of vein growth, as 
is indicated by the veins sketched in Fig. 2. Other veins are roughly 
banded, with pyrite along the walls and calcite in the center (see 
