8 T. STERRY HUNT ON THE GENETIC 
regards the Secondary or Tertiary age of crystalline stratified rocks, we are naturally led 
back to the nomenclature of Werner and his school, which should be equally acceptable 
to endoplutonists and to neptunists, whether the latter adopt the Chaotic hypothesis set 
forth by De la Beche and Daubrée, or the Crenitic hypothesis more recently maintained by 
the present writer in the essay just cited. 
§ 2. The term “crystalline rocks” is conveniently used in geology to designate those 
original aggregates of which crystalline silicates make an essential part. Such silicates 
may, however, be associated in these aggregates with quartz, or with oxyds like magne- 
tite, with carbonates, as in limestones and dolomite, and even with phosphates, as apatite, 
or with sulphates, as karstenite and gypsum. By a certain license the term may also be 
extended to masses of definite hydrous silicates, such as serpentine and pinite, which 
are in great part amorphous and colloidal, and also to uncrystalline silicates, often 
hydrated, and of indefinite composition, such as palagonite, tachylite, pitchstone, and 
obsidian. The silicates having the composition of serpentine and of pinite assume, in 
some cases, proper crystalline forms; palagonite is by heat readily changed in large part 
into a crystalline zeolite; while glassy silicates, such as obsidian, by devitrification, are in 
like manner resolved more or less completely into crystalline species. Hence rock-masses, 
including or even made up of these various uncrystalline materials, may all be regarded 
as inchoately crystalline, and for geognostical purposes may be conveniently classed with 
the crystalline rocks into which they graduate. 
§ 3. When stratified masses of quartz, calcite, dolomite, and karstenite are found 
among contemporaneous crystalline silicated rocks, they generally enclose indigenous 
erystalline silicates, which give them a title to be regarded as parts of the accompanying 
crystalline series. The mineral species just named have, however, in other cases become 
aggregated in crystalline rock-masses in times and under conditions which did not permit 
the genesis of such species as feldspars, micas, amphibole, and pyroxene, which are the 
most characteristic silicates of the crystalline rocks. Hence we find beds of crystalline 
quartz, limestone, dolomite, karstenite, and gypsum interstratified with uncrystalline 
rocks of detrital origin, and of Secondary or Tertiary age. It is worthy of note, however, 
that the conditions for the production of certain mineral silicates have continued in later 
ages, as is Shown by the frequent formation of zeolitic, pectolitic, and other crystalline 
silicates in younger and uncrystalline rocks, and even down to our own time, and, more- 
over, by the occurrence among uncrystalline sediments of later geological periods, of de- 
posits of serpentine, sepiolite, and glauconite. The history of both zeolitic and pectolitic 
silicates (as formed by secretions in basic rocks, and as generated in deep-sea ooze, and in 
the channels of thermal waters,) has been discussed at some length in the preceding essay, 
but there are facts in relation to the other silicates just mentioned which are of such im- 
portance in connection with the origin of crystalline rocks as to merit consideration in this 
place. 
§ 4. Two examples of crystalline silicates related to zeolites in composition, which 
are found injecting organic remains remains in palæozoic limestones, have been observed 
by Sir J. W. Dawson, and were farther described and analyzed by the present writer in 
1871. The first of these is from a Silurian limestone which is found near Woodstock, in 
the province of New Brunswick, and consists almost wholly of comminuted organic re- 
mains, including fragments of trilobites, gasteropods, brachiopods, and joints and plates of 
