32 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [NoV. 29, 



to the eastward and westward. Detached hills occasionally take the 

 place of the spurs, and the direction of these is in one instance pro- 

 longed by a chain of islands extending in a line parallel with the main 

 range. 



In several places the continuity of the main range ceases, and 

 detached hills of an equal height flank the gap. A second range, 

 however, rises after the interval of a mile or more, and is prolonged 

 in the general direction of the first. 



On the western side of the peninsula the Harbours of Mauaia, 

 Tekouma, and Coromandel are formed by the jutting out of spurs 

 from the central range. 



Geology of the District. — In a country covered with so dense a 

 forest as that of the wooded districts of New Zealand, and where 

 there are no artificial cuttings, sections showing the geological struc- 

 ture are but few ; and anything farther than a slight sketch of the 

 geology must be the result of more extensive observation than time 

 and circumstances have yet enabled the writer to give to the subject. 

 Judging from what has actually been observed, and without assuming 

 the existence of any rock in a place in which it has not been seen, 

 the following may be stated. 



The predominating rock in the whole of the principal range and 

 most of the subordinate hills appears to be a decomposing breccia 

 (Specimens marked A.) *. This breccia, of which variously-coloured 

 granites and red porphyry (Specimens A. *) are the chief components, 

 mainly forms the sides of the range of the spurs, together with the 

 detached hills and outlying islands. The highest points of the main 

 range, generally precipitous crags, are of granite (Specimens B,). 

 Where the water-courses have cut deep into the sides of the ridge, 

 slate (Specimens C.) is exposed, of a blue or dark grey colour, and 

 with a varying dip and strike. Trap and quartzose veins are very 

 prevalent ; and indications of copper (Specimens D.), iron (Speci- 

 mens E.), and silver are common. Quartz veins, of a breadth from 

 half an inch (Specimens J.) to that of 15 feet, traverse the slate and 

 breccia, and generally run in a direction similar to the trend of the 

 main range, of which in some cases they form the crest. "Where the 

 spurs from the range follow an easterly or westerly direction, the 

 quartz veins intersect them, still in parallelism with the range. 



On the western coast, at distances of 4 and 6 miles from the main 

 range, a granite appears, of a character somewhat approaching to that 

 of gneiss, together with clay-slate. The relation of these formations 

 with the main ridge has not yet been traced. 



On the eastern side of the peninsula is an extensive district com- 

 posed of indurated pumice-sand, which from the rounded form of its 

 grains, and the horizontal position of its layers, appears to have been 

 deposited below the sea, and to have been subsequently elevated. 

 The indentation of Mercury Bay, with its rivers, is the division be- 

 tween this formation and the crystalline rocks of the main range. 



To the westward, at a distance of about 30 miles (across the Thames 

 Frith), is the volcanic formation of Auckland ; the clay-slates of 

 * The specimens referred to in the paper are in the Society's Collection. 



