286 



Transactions. 



Art. XXXI. — Note on the Mechanical Composition of the So-called 



Loess at Timaru. 



By L. J. Wild, M.A , B.Sc, F.G.S., Canterbury Agricultural College. 



[Read before the New Zealand Institute-, at Christchurch, 4th-8th February, 1919 ; received 

 by Editor, 12th February, 1919 ; issued separately, 16th July, 1919.] 



The origin of the so-called loess at Timaru, and of other similar deposits 

 on Banks Peninsula and elsewhere in tlie South Island, is connected with 

 the larger problem of the formation of the Canterbiiry Plains, and with 

 the question of the direction of the more recent movements of the land 

 in that area. Haast* was of opinion that the deposit is similar in origin 

 to the loess of China described by Baron von Richthofen — that is to say, 

 it is an aeolian deposit. In this opinion he has been supported by Hard- 

 castle, f by Speight,"! and by Professor A. Heim§ of the University of 

 Zurich. Marshalljl has also declared his adhesion to Haast's view. Hutton^ 

 always strenuously opposed this theory, maintaining the deposit to be a 

 marine silt laid down during a period of submergence of the plains ; and 

 he quotes Professor Boehm, of Freiberg, in support of his arguments. 

 Since analyses of the deposit as seen typically at Timan; may shed some 

 light on the problem I submit this note, though I "admit my contribution 

 of original observations is small when the importance of the question and 

 the time given to it by previous workers are considered. 



The following results were obtained by the method of mechanical 

 analysis adopted by the British Agricultural Education Association (see 

 Journ. Agric. Science, 1906, vol. 1, p. 470). The particles are freed from 

 one another by treatment first with dilute hydrochloric acid to dissolve 

 inorganic cements, then with dilute ammonia solution to dissolve organic 

 cements. They are then separated by sedimentation. 



Table I. — Mechanical Analyses of Samples of the So-called Loess at Caroline 



Bay, Timaru. 



* J. VON Haast. Geology of Canterbury and Westland, Christchurch, 1879. 

 t J. Haedcastle, Trans. N.Z. Inst., vol. 22, p. 406, 1890. 



t R. Speight, Trans. N.Z. Inst., vol. 40, p. 33, 1908; Trans. N.Z. Inst., vol. 49, 

 p. 386, 1917. 



§ A. Heim, Quoted by Speight, Trans. N.Z. Inst., vol. 40, p. 33, 1908. 



II P. Marshall, New Zealand and Adjacent Islands, p. 31, Heidelberg, 1912. 



11 F. W. HuTTON, Trans. N.Z. Inst., vol. 37, jj. 465, 1905. 



