1896. | NEW YORK ACADEMY OF SCIENCKS. - 269 
factory. A quarter of a mile to the southwest another sheet of 
gneiss presents similar relations to the limestone, and here again 
the contact is marked by an extensive development of pyroxene 
and scapolite, although the mass has never been opened up. The 
general relations of these deposits are so like those shown by 
the typical cases of contact metamorphism that the conclusion 
is at once suggested that they have been formed by the same pro- 
cess. This supposition requires that the intrusive rock now rep- 
resented by the gneiss should have undergone considerable modi- 
fication ; but this isso commonly the case with the igneous rocks 
of the region that no difficulties are presented. Nevertheless, 
while there is evidence in favor of the formation of the minerals 
by contact metamorphism, the case is an extremely doubtful one. 
Another explanation suggests itself as applicable and equally, if 
not more, probable. According to this,the minerals may result 
from the mingling of the silica,alumina, iron and alkalies of the 
gneiss with the lime and magnesia of the limestone, and the crys- 
tallization of the minerals during regional metamorphism. The 
mingling of materials might be original, resulting from the grad- 
ual change of one kind of sediment into another; or secondary, 
being produced by circulation of water during metamorphism. 
It is conceivable that, under such conditions, an association of 
minerals might be produced quite similar to those resulting from 
an intrusion, particularly if the regional metamorphism involved 
high temperatures. The apparent gradation between the gneiss 
and the limestone is certainly in harmony with this view. La- 
croix,* who has described the locality, seems to incline to 
this explanation, though he finds reason for believing that the 
gneiss itself has been modified by a granite intrusion not ex- 
posed at the surface. 
The Wells farm in Pierrepont affords another locality where 
the relations are similar to those last described. The minerals 
are amphibole, of a green-gray tint, pyroxene, oligoclase, and 
quartz. The first mentioned species occurs in perfect crystals 
and radiating aggregates of much beauty. Here, the minerals 
form irregular masses on the contact between limestone 
and a rather acid gneiss. The latter rock is of a type which, 
though somewhat obscure in character, is, for many reasons, re- 
garded by the writer as of igneous origin. At this point it may 
well be the contact facies of a coarse porphyritic granite-gneiss 
exposed a few rods to the north. Between the gneiss and lime- 
stone there is not, as at the previous locality, any trace of 
gradation, although two bands of gneiss appear with the lime- 
stone lying between. This structure might result equally well 
*Op. cit. p., 184, 
