Hutton. — On a Leucophyre from the Setwyn Gorge. 271 



other places they are twisted, contorted, and broken off in all 

 maimers of ways ; in fact they resemble in this the laminated 

 rhyolites so common about Lake Taupo. The specific gravity 

 is about 2-53. I have only prepared thin sections of one speci- 

 men, as they are extremely hard, and more are not necessary for 

 my present purpose, which is merely to draw attention to the 

 existence of these rocks. This specimen is one of those with 

 pink laminae, and it shows under the microscope the ordinary 

 felstone structure, with a mosaic between crossed nicols, which 

 vanishes when the nicols are oblique. The pink bands are due 

 to minute specs of ferric oxide in a more opaque base. I should 

 judge that the original lava contained two magmas differing in 

 their amount of iron oxide, and that in the more ferriferous 

 lamina? some of the iron has segregated into minute globules. 



There can be no doubt but that all these rocks are devitrified 

 rhvolitic lava streams. 



Art. XXXV. — On a Leucophyre from the Sehvy?i Gorge. 



By Professor F. W. Hutton, F.G.S., and G. Gray, F.C.S., 

 Lecturer on Chemistry at the School of Agriculture, Lincoln. 



[Read before the Philosophical Institute of Canterbury, Qth October, 1887.] 



This rock was first noticed by Sir James Hector, as greenstone 

 (diabase ?) occurring in the gorge of the Wakaepa (or Selwyn) in 

 the Malvern Hills," and is shown on his section (I.e., iv. c.) 

 as interbedded with slate rocks, and forming an anticlinal. Sir 

 Julius von Haast, m his " Eeport on the Geology of the Malvern 

 Hills," mentions them under the name of diabasic rocks, t as- 

 sociated with chertsose rocks and marble. Also in his " Geology 

 of Canterbury and Westland," (p. 271) as diabase ash-beds. In 

 " Keports of Geological Explorations for 1883," p. 29, Mr. S. H. 

 Cox mentions these diabases, and says that he agrees with Mr. A. 

 McKay that they are the same as the diabase ash-beds and cherts 

 of Okuku which he had found to contain triassic fossils J Mr. 

 A. McKay in " Geological Keports, 1884," (Bulletin of Geological 

 Survey, No. 1,) p. 7, describes them as diabasic rocks with 

 jasperoid rocks, either slates or resembling tufaceous sandstone, 

 grey or reddish limestone, crystalline or compact at different 

 horizons in the diabasic beds, with grey cherts and manganese 



* " Rep. Geol. Expl." 1870-71, p. 49. 



t " Rep. Geol. Expl." 1871, p. 136 ; and 1871-72, p. 10 



\ " Rep. Geol. Expl." 1879-80, p. 99. 



