396 Geological Society : — 



1 he Arithmetic of Electrical Measurements. By W. R. P. Hobbs, 



E.N., A.I.E.E. Seventh Edition. London:' Thomas Murby. 

 This book contains a good collection of arithmetical exercises on 

 Ohm's law and its applications, including such subjects as resistance 

 of divided circuits and partition of current in them, best arrange- 

 ment of cells and measurement of the electromotive force of cells. 

 The exercises are preceded by a few fully-worked examples in each 

 section, and answers are given in all cases. That the volume 

 supplies a want felt by many electrical students is evidenced by its 

 having reached a seventh edition ; it is now issued in a revised 

 form with a new section devoted to questions connected with 

 electric-lighting and power. J. L. H. 



XLII. Proceedings of Learned Societies. 



GEOLOGICAL SOCIETY. 

 [Continued from p. 317.] 



May 24th, 1899.— W. Whitaker, B.A., F.R.S., President, 

 in the Chair. 

 r PHE following communications were read : — 

 -*■ 1. 'On the Distal End of a Mammalian Humerus from Ton- 

 bridge.' By Prof. H. G. Seeley, F.R.S., F.G.S. 



2. ' On Evidence of a Bird from the "Wealden Beds of Ansty 

 Lane, near Cuckfield.' By Prof. H. G. Seeley, F.R.S., E.G.S. 



8. ' Notes on the Rhyolites of the Hauraki Goldfields (New 

 Zealand).' Bv James Park, Esq., E.G.S., and Frank Rut ley, Esq., 

 E.G.S. ; with Analyses by Philip Holland, Esq., E.I.C., F.C.S. 



Part I. of this paper, by Mr. J. Park, gives a description of the 

 rhyolites as seen in the field. After a rest from volcanic action 

 during the Secondary Period, the Tertiary eruptions burst forth 

 and were more widespread than those of recent times. In the 

 Hauraki Peninsula the basement Palaeozoic rocks are covered by 

 richly fossiliferous marly clays and limestone of Lower Eocene age, 

 and these by a vast accumulation of andesitic lavas and tuffs, 

 in places 3000 feet thick. These andesites are the gold-bearing 

 rocks of the district, and they are succeeded by rhyolitic lavas and 

 ashes. Both andesites and rhyolites were influenced by solfataric 

 action, resulting in siliceous deposits rich in gold and silver. The 

 rhyolites rest on rocks probably of Upper Miocene age, and are 

 followed by Pleistocene and recent deposits ; so that they probably 

 range from older to newer Pliocene in date. 



Part II. contains the observations of Mr. Rutley on the petrology 

 of the rhyolites. The rocks present occasional occurrences of 

 perlicity, and the lithoidal types sometimes owe their characters to 

 subsequent devitrification, sometimes to the effect of cooling on, or 

 immediately after eruption. Reheating has at times reduced the 

 felspars to the condition of felspar-glass. Although plagioclase- 

 felspar is common, the analyses indicate that the series must be 

 retained with the rhyolites, it being quite possible that some of 

 these minerals may have been derived from the andesites. In 



