356 



C. A. COTTON 



basic, volcanic rock varying in size, the largest noted being 4 ft. 

 in diameter, and by very rare, small pebbles of a iine-grained, 

 porphyritic rock with small felspar phenocrysts. 



Successive bands of conglomerate vary in coarseness, but there 

 is no definite alternation or succession of coarser and finer strata. 

 One conspicuously coarse band which occurs about 40 ft. from the 

 base of the section in the main branch of the Dee is shown in Fig. 5. 

 The large bowlders of which it is mainly composed are derived 



principally from the younger 

 rocks, but large "Maitai" 

 pebbles, up to 6 ins. in diameter, 

 are present, and there are some 

 rounded bowlders up to 6 ft. in 

 diameter which may be either 

 Cretaceous or pre-Cretaceous. 



In the gorge of the Mead. — -In 

 the Mead gorge the conglomerate 

 is, on the whole, coarser than in 

 the Dee, and here, more than 

 anywhere else where it was ex- 

 amined by the writer, there is a 

 mixture of fragments of all sizes. The very largest are rare, but 

 blocks up to 2 ft. in diameter are common, and about one-third of the 

 bulk is composed of bowlders over 6 ins. in diameter. All of them 

 are water worn and most are fairly well rounded. Small pebbles are 

 very abundant throughout, the majority of them being as small 

 as or smaller than a hen's egg. They are fragments of the hardest 

 of the pre-Cretaceous or "Maitai" rocks, smooth and well rounded, 

 frequently almost spherical. There is in addition, both here and 

 in the Dee, a large proportion of fine, sandy material filling the 

 interstices, and the conglomerate is cemented into a very hard rock. 

 The rocks represented are: large bowlders of the same coarse- 

 grained, basic, volcanic rock that occurs in the Dee section; smaller 

 and much rarer fragments of the fine-grained porphyritic rock also 

 sparingly represented in the Dee; blocks of fine, Tertiary sandstone 

 up to 2 ft. in diameter, crowded with shells and water worn (these 



Fig. 5. — Coarse band in the Great 

 Marlborough Conglomerate in the Dee 

 gorge. View looking southwest. 



