122 W. WHITAKER ON TELE RED CRAG. 



6. Note on the Red Crag. By William Whitaker, B.A., F.G.S. 

 (Read November 8, 1876.) 



(Communicated by permission of the Director General of the Geological 

 Survey of the United Kingdom.) 



My work on the Geological Survey in the Crag District has led me 

 to think that previous observers have made a slight error in the 

 classification of a certain ferruginous sand that is often to be seen 

 above the shelly Red Crag, the line of junction being mostly very 

 irregular. 



This sand has been described by Prof. Prestwich as an " upper 

 division " of the Red Crag, or, to quote his own words, " owing to 

 the want of all fossils in the neighbourhood of Ipswich, as the ' un- 

 productive sands ' of the Red Crag " * ; and he goes on to speak of 

 the " erosion of the -lower division " underneath this, afterwards 

 classing the upper with the Chillesford sands t. 



Mr. S. Y. Wood, Jun., has referred the ferruginous sand in ques- 

 tion to various horizons in the Glacial Drift, I believe with a con- 

 stant tendency to lower its horizon ; but his former views need not 

 be dwelt upon, as that tendency has continued until he has accepted 

 my classification, and now regards this sand simply as Red Crag, 

 not separated stratigraphically or palseontologically from the shelly 

 mass below. 



The so-called " eroded " surface of the shelly Crag, noticed by 

 various observers, is, indeed, apparently so only ; bat I must say 

 that in many sections there is little or nothing to throw doubt on the 

 reality of the appearance, which is somewhat analogous to the " mi- 

 micry " sometimes seen in insect life, though in our case one cannot 

 see any object to be served by the delusion, unless it be the bewilder- 

 ment of geologists. An examination of a large number of sections, 

 however, and an attention to mere local details that could hardly be 

 expected from any one but an observer who is obliged to note them 

 as a matter of business, has conclusively shown that we have in this 

 case not an eroded surface, worn out in a lower before the deposi- 

 tion of a higher bed, but an occurrence akin to the " pipes " of sand 

 &c. so often seen piercing the top of the Chalk, and which, too, have 

 also been taken as evidence of erosion, though their origin is now 

 well understood : we have, in fact, an irregular underground sur- 

 face, caused by the dissolving action of carbonated water in per- 

 meable beds, a surface formed after the deposition of the upper 

 beds by the dissolving away of the shells that they once contained. 



That the above is the true explanation of the irregular removal 

 of the shells was first suggested to me by the fact that the apparently 

 unfossiliferous sand above is, for the most part, exactly like the 

 sand of the shelly Crag below, differing only in the absence of 

 shells. Confirmatory evidence was given by the not uncommon 

 occurrence in the upper sand of layers or masses of ironstone or 



* Quart. Journ. Geol. Soc. vol. xxvii. p. 333. t Ibid. pp. 336, 338. 



