78 BASIC AND ULTRABASIC IGNEOUS ROCKS— BENSON. 



In conclusion, the author desires to acknowledge his indebtedness to many geologists of 

 whom he would specially mention five. The broad significance of the problem discussed first 

 was made clear to him by Suess's great work. The writings and personal encouragement of Prof. 

 Daly have been most stimulating, and the significance of Bowen's invaluable experimental 

 work and discussions will be obvious. To his teachers, Prof. Sir Edgeworth David, of Sydney, 

 and later Doctor Harker, of Cambridge, the writer's indebtedness can not be fully measured, but 

 he desires gratefully to acknowledge that whatever of value may be found in the present work 

 owes its inspiration very largely to their influence and encouragement. 



POSTSCRIPT. 



The manuscript of this memoir was finished in November, 1919, and was accepted for 

 publication twelve months later, some additions being made in the interval. Further material 

 was incorporated in order to bring certain portions more up to date, when the proofs were being 

 corrected in September, 1922, but there was not the opportunity of considering fully the bearing 

 on the subject of Bowen's reaction-principle which had just been published. (Journ. Geol. 1922, 

 pp. 176-198.) Similarly there can not now be utilized the results of the recent revision of 

 the geological features of the Bushveld Complex, though they are of great importance in this 

 connection. (See Daly, R. A., and Molengraaff, G. A. F., Journ. Geol., 1924, pp. 1-35, and 

 Wagner, P. A., Memoir 21, Geol. Surv. Union of S. Africa, 1924. Another memoir in this series 

 dealing with the whole complex is being prepared by A. L. Hall.) Briefly, the facts announced 

 show that the great mass of basic and ultrabasic rocks was injected into the upper portion of the 

 Pretoria series, and not between this and the Waterberg series. (See pp. 47-49 and 73 above.) 

 It was intimately associated with intrusive masses of syenite and granophyre, and with felsites 

 that seem to have broken through to the surface, and was gravitationally differentiated approxi- 

 mately in the manner explained by Bowen in various papers, though a special explanation of 

 the origin of the banded structure in this mass is suggested by Wagner. The red granite 

 is clearly younger than the basic rocks which it invades, though older than the Waterberg 

 sediments which rest on its eroded surface. Subsequent faulting has caused portions of the 

 granite to project into these sediments and such were formerly accepted as being definitely 

 intrusive apophyses. 



