IO FRANK D. ADAMS 
abundance varying from slide to slide. ‘The polysynthetically twinned 
plagioclase in some cases equals the potash feldspar in amount, but 
usually the potash feldspars seem to be rather more abundant. 
The Quartz is found only in a few of the thin sections and is there 
present only in very small amount. 
When the Calcite survives, it can be seen that the original rock had 
the character of a coarsely crystalline limestone or marble. Under 
the action of the metamorphic processes the silicates have grown into 
it in the form of rounded grains which, increasing gradually in size, 
have finally left the calcite merely as a filling of the surviving inter- 
stitial spaces. The grains are about the same size as those of the 
other minerals. 
An examination of thin sections of a suite of specimens of this 
amphibolite from a single series of exposures in the cutting on the 
line of the Irondale, Bancroft and Ottawa Railway at Maxwell’s 
Crossing—some of them still containing little surviving bands of calcite 
and others of the harder and more altered varieties—shows that in 
the former pyroxene and scapoiite accompany the hornblende and 
feldspars, while as the alteration becomes more pronounced these 
former minerals become less abundant and eventually disappear, 
giving rise to a rock composed of hornblende and feldspar, associated 
with which a little biotite is seen in some specimens, with certain 
accessory minerals which are common to both rocks. Although, as 
above mentioned, no actual passage. of pyroxene into hornblende 
could be definitely observed, the hornblende individuals often have 
a minutely serrated edge where they come against the pyroxene, as 
if they were gradually enlarging themselves at the expense of the 
latter mineral and thus replacing it. 
The amphibolite, representing the final product of the alteration, 
while possessing a more or less distinct foliation, has the “ pflaster,”’ 
“pavement,” or mosaic structure characteristic of rocks which have re- 
sulted from recrystallization brought about by metamorphic processes. 
It presents no evidence of crushing or of having been caused to move 
since its recrystallization took place. ‘This structure is quite distinct 
and different from that seen in the little injected bands of granite. 
In these, which are composed of quartz, microcline, orthoclase, and 
plagioclase, the quartz occurs for the most part in thin leaves with 
