Geology of Nllhihcootlr. 291 



lielow the junction of Back Creek witli the Broken River the 

 conglonierato widens nut, and can be traced some distance doiwn 

 the Htreani, but finally <^ives place to alluvium and resorted boul- 

 ders friiin the conglomerate. About a mile and a Imlf lic-iow tho 

 junction a narrow belt of conglomerate joins the main nui*s on 

 the east. Tliis tributary portion is considerably dissected, but 

 the whole surface of the ground is covered with ferns and scrub, 

 so that very little can bo seen of the nature of the material. 



The evidence in fjivour of this conglomerate being of glacial 

 oriirin is a.s follows: — ■ 



(1) Miiiiy of the l>oulders are facetted, smootliLMl iuid polislied, 

 and are gfiierally quite unlike water-worn material. Here and 

 there blocks are seen having a pdHioii of its surface smoo) lic.<l, 

 but the remaindei' ia rough and angular. 



(2) The composition of the boulders, found in the conglomerate 

 ia of an extremely varied character, and although most of them 

 can be matched with the rocks in the district, some are quite 

 distinct from any known rocks in this vicinity, and have probably 

 travelled a considerable distance from the place from which they 

 were derived. 



(3) Tlie composition of the boulders seems to V>ear no relation 

 to the composition of the underlying rock, i.e., a change in the 

 composition of the underlying rock causes no change in the 

 relative proportions of the various types of rocks contained in 

 the conglomerate. 



(4) The matrix seems to va,ry with the composition of the 

 underlying rock, being fine grained and seemingly composed of 

 ground-up sedimentary rooks, where the conglomerate rests on 

 the siltu'ian. Whereas angular (piartz is fairly abundant through- 

 out the matrix, where the bedrock consists of granite. 



(5) Microscopic sections of the matrix show that the consti- 

 tuent grains are angular to subangular, and so arc distinct from 

 rounded water-worn grains. 



(6) The distribution of the conglomerate, especially below the 

 junction of Back Creek and tlio Broken River, wiiere it is over 

 half a mile in width, and alMiut 70ft. in thickness, can be easily 

 explained if we accept the glacial origin of the conglomerate. If 

 the conglomerate be not due to glacial action, then it must be 

 of river formation. From the site originally proposed for the 



20A 



