182 TRANSACTIONS OP SECTION C. 



of the number of students of mining and economic geology who receive their 

 training in this country and ultimately go out into the world to find themselves 

 face to face with problems in which a true understanding of the local geology 

 is absolutely essential. 



I shall not discuss here the important subjects of the indexing of 

 geological literature and the preparation of abstracts of current publications. 

 The former is already being efficiently dealt with by the Geological Society, 

 and the latter will, I trust, be provided for in some way in the immediate 

 future. 



I now proceed to indicate some lines along which it seems to me probable 

 that there are opportunities for progress in geological research. 



In the investigation of the sedimentary rocks attention has been usually 

 directed mainly to the larger and more obvious features, and these have sufficed 

 to afford considerable insight into the conditions which prevailed when they 

 were laid down. The detailed study of the minor structures or texture of 

 these rocks by lens and microscope has, on the other hand, been comparatively 

 neglected, though it is capable of affording us valuable information that could 

 be obtained in no other way. There are, however, I need hardly say, important 

 exceptions, the classical researches of Sorby extending over more than half 

 a century, the investigations of Hutchings on the argillaceous rocks, and much 

 useful work in recent years on the mineral constituent* and microzoa of the 

 sedimentary rocks generally. But, although individual sediments have been 

 carefully studied, few, if any, attempts have been made to carry out a detailed 

 examination of the successive beds of a stratigraphical succession comparable 

 to the systematic zoning by means of fossils which has yielded such valuable 

 results. 



Not only ought the texture and composition of the individual laminae to be 

 patiently studied to obtain information as to the exact manner of their deposition, 

 but attention should be more especially directed to the character of the trans- 

 ition by which one layer gives place to another, so as to determine, if possible, 

 the cases where there has been a gradual passage without a break, and those 

 in which there has been a pause in the deposition of greater or less duration, 

 or even a removal of material, although nothing in the nature of an uncon- 

 formity, however slight, can be detected. Even in apparently uniform deposits, 

 such as chalk and clay, variations in texture and composition may be brought 

 out by special treatment and reveal interesting details of the conditions under 

 which they were deposited. 



It is of special importance to recognise and examine in detail the occurrence 

 of rhythmic repetitions of a similar succession of sedimentary materials and 

 characters. A single cycle in such a succession may be only a twentieth of an 

 inch in thickness, as in the case of ferruginous banding in the Lower Hangman 

 Grits at Smith's Combe in the Quantocks, or may include thirty or forty feet 

 of strata, as in the Caithness Flags. Rhythms have been described from the 

 pre-Cambrian of Finland, the Ordovician of North America, 15 the Permian 

 of Stassfurt,"' the Cretaceous of Arkansas,'' and the Quaternary of Scandinavia 

 and Palestine, and many more, no doubt, occur in the stratigraphical succession 

 of different countries. It would probably be found that a similar repetition 

 occurs in fine terrigenous deposits off the coast of tropical countries where there 

 is a well-defined alternation of wet and dry seasons. In some places minor 

 cycles may be superimposed on larger, as in the ca.se of the Skerry Belts 

 described by Bernard Smith '" in the Upper Keuper of East Nottinghamshire. 

 The general question of the significance of such rhythms of stratification must, 

 liowever, be reserved for another occasion. 



It is more difficult to arrive at the true interpretation of the phenomena 



'^ Joseph Barrell ; Bull. Geol. Soc- Am., vol. xxviii., pp. 789-90, 1917. 

 1° G. Ochsenius ; Zeitsch. fiir practische Oeologie. vol. 13, p. 168, 1905. 

 " G. K. Gilbert; Journ. of Geology, vol. iii., pn. 121-127. 

 >» Geol. Mag., 1910. pp. 303-305. 



