736 THE TIN-DEPOSITS OF NEW ENGLAND, N.S.W., I., 



The granite hills are more rounded and less precipitous than 

 those in the slate country, and usually more soil is present. It 

 is not uncommon, however, to find very large areas of bare rock 

 generally steeply sloping on the side of a hill. (See Plate lix., f ig. 1 ). 

 This is a very prominent characteristic of the granite hills at 

 Howell. Here, many of the hillsides consist of clean bare rock 

 of a reddish color, and the whole presents a most striking 

 appearance. This feature I have always observed to be developed 

 on the northern slopes of the hills, where changes of temperature 

 and rock-disintegration are most rapid. 



The coarser-grained types of granite are more prone to 

 decomposition than those of finer grain, and hence the higher 

 granite hills are usually of the latter kind. The porphyritic 

 granite is the most prone to decomposition, the phenocrysts 

 becoming dislodged, before being appreciably decomposed, by the 

 disintegration of the finer matrix surrounding them. 



The basalts constitute the youngest rocks, are seen to overlie 

 slate and granite alike, and to fill in the pre-basaltic valleys and 

 watercourses. There is considerable variety in the basalts* 

 and the relative resistance to weathering of consecutive flows 

 frequently gives rise to a terrace-like structure on the slopes of 

 the basalt-hills. This is well developed in the neighbourhood of 

 Elsmore. Conical basalt-knobs are not infrequent, but are much 

 rarer than in most volcanic areas. A much more common feature 

 is the very striking development of long level-topped ridges of 

 basalt terminating rather abruptly in steeply sloping ends. This 

 suggests that the outpourings of the lavas are related to fissures 

 rather than to foci of eruption. 



The river-system is consequent. The fall in the general surface 

 of the country is to the west, the rate of fall being about 1000 

 feet in 30 miles. One marked feature is the development of 

 the streams along the junction of geological formations and lines 

 of structural weakness. Streams have been noticed flowing for 

 quite a distance along, or close to and parallel with, the junctions 

 of granite and basalt, of basalt and slate, and also of slate and 

 granite. The pre-basaltic stream-courses were subject to the same 



