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 tlieir 

 material are tlie oldest. 



The rocks of tlie Primary class in the tiiird district arc few in number ; they arc of gneiss 

 and granite cliiefly, 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 

 tlie district. 



The rocks of the Transition class in the third district arc readily, distinguished from those 

 of the Primary class, by difference of position when both are 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. Tlie 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 fonned of terrene origin. All the species of organic bodies contained in 

 this class are wholly extinct, many of the genera also, a number of whicli 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 difierent kinds 

 of rocks which were found in the district, and especially those of tlie Transition class, being 

 the most important ; to note their mineral and fossil characters and associates, or products ; 

 llie order in which the rocks or masses follow each other, as to age or superposition ; and to 

 group those together which intennix, or are connected by common characters. In this report 

 the lenn group is synonymous with formation, which is not used, from liaviiig a twofold 

 signification, and of a kind which tends to confuse the subject. 



