494 J. P. Kimball—Geological Relations and Genesis 
only at the surface of such bodies as shown by the prevalence of 
float of ferric oxide remarkably pure, but evidently from small 
plates or segregations on their sides. arnetiferous aggregates 
with considerable proportions of specular and magnetic oxides 
of iron are the most common products of metasomatism met 
with on the dioryte summits. 
The marble ledges have, however, so many relations in com- 
mon with the iron-ore bodies, the coralline parentage of which 
seems to me demonstrated, that they likewise must be referred 
to a similar primary origin. Their metamorphism or crystal- 
lization is due to igneous contact. Their preservation in the 
metamorphic state without metasomatic alteration, is explained 
as above by their obvious exclusion from the conditions which 
have governed the alteration into ferric oxide of other coral- 
lines, whose more favorable environment with reference to 
such an alteration, I now proceed to describe. 
Toward the continuous base of the second range of hills the 
locally given way to darker complexions of red. and brown, 
especially in such as exhibit a notable proportion of free silica, 
and a dense amorphous consistency. Aggregates of clear crys- 
talline quartz in admixture with magnetic oxide of iron like- 
wise occur, apparently as residual forms of the alteration under 
local circumstances of basic material originally containing a 
notable proportion of this oxide. 
The syenyte conspicuously outcrops in contact with ore-bod- 
ies only ina single instance. This is the south ore-body of East 
' Mine Hill. Here one side and both ends of the ore-boss abut 
upon the syenyte, which thus forms a cul-de-sac. The contact 
upon the exposed side is occupied by two courses of rotten, 
aluminous and bleached chlorite in a kaolinized state. These 
are succeeded by a plate of amorphous siliceous and highly fer- 
masses ; another part the alteration in situ of ramifications 
or tongues of diorytie eruptive material intruded into frac- 
