10 
GEOLOGY OF THE THIRD DISTRICT. 
the base or support of all the other classes, being inferior in position and consequently supe¬ 
rior in age. They may be confounded with some of the volcanic rocks, as these are more or 
less crystalline, and contain neither organic remains nor rolled stones — the materials of which 
were derived from a lower position than the known primary rocks, and as respects their 
material are the oldest. 
The rocks of the Primary class in the third district are few in number; they are of gneiss 
and granite chiefly, also of hornblende rock, primary limestone, and a few rare, partial aggre¬ 
gates of coccolite and table spar, the last rocks covering but very small portions or patches of 
the district. 
The rocks of the Transition class in the third district are readily distinguished from those 
of the Primary class, by difference of position when both arc present; by the former being 
in regular layers, more or less flat or horizontal, and apparently undisturbed ; some appearing 
as if deposited as sediment, like mud, sand, gravel, &c. whilst others were separated from a 
solvent in the manner of lake marl. The greater number abound in organic remains, chiefly 
of sea shells or testaceous bodies, corallines, &c. also of marine plants or fucoides; a few 
only having been formed of terrene origin. All the species of organic bodies contained in 
this class are wholly extinct, many of the genera also, a number of which ceased to exist 
before the coal was formed. The greater part of the surface rocks of the district are of this 
class, and it is the most important class in every respect in the district. 
The Quaternary class comprises clay, sand, loam, gravel, boulders, lake marl, calcareous 
tufa, bog ores, peat and soil. These products rest upon either, or both of the other classes, 
being superficial deposits. 
In prosecuting this survey, the first object was to ascertain what were the different kinds 
of rocks which were found in the district, and especially those of the Transition class, being 
the most important; to note their mineral and fossil characters and associates, or products ; 
the order in which the rocks or masses follow each other, as to age or superposition; and to 
group those together which intermix, or are connected by common characters. In this report 
the term group is synonymous with formation , which is not used, from having a twofold 
signification, and of a kind which tends to confuse the subject. 
