730 MR. E. W. HARMER ON THE CRAG OP ESSEX. [Nov. I9OO, 



The marked difference between the shelly marl of the Coralline 

 Crag, containing only about 12 per cent, of exceedingly fine in- 

 organic material, and the much coarser quartzose sands of the 

 lied Crag, points to some change in the geographical conditions of 

 the Crag basin. In the Coralline Crag, we have the spoil of the 

 sea-bottom, principally organic : shells and shell -fragments heaped 

 up in submarine banks by currents ; in that of the Eed Crag, there 

 is, in addition to shelly debris, a large percentage of inorganic 

 material derived from coast-erosion, and sediment brought down 

 by rivers, which afterwards accumulated against, or near to the 

 shore. 



In a paper which I have quoted on a former occasion, 1 Mr. W. H. 

 Wheeler gives his reasons lor believing that in our shallow seas at 

 the present day very little permanent movement of sand derived 

 from coast-waste takes place below low-water mark, the coarser 

 part of such material only being carried along the shore by tidal 

 action, and, further, that the supply of such littoral drift is ex- 

 ceedingly limited. If this be so now, when mauy parts of the 

 English littoral are fringed by cliffs of Glacial sand and sandy clay, 

 still more must it have been so in East Anglia during the Later 

 Pliocene Period, when strata of Eocene clay formed the margin of 

 the lied Crag sea. It does not, therefore, seem probable that the 

 waste of the land by wave- action could, of itself, have supplied 

 material for the inorganic portion of the enormous mass of sandy 

 Crag which covers so much of Suffolk and Norfolk. There is no 

 evidence that any river entered the English Crag area during the 

 deposition of the Gedgravian Beds, but the contrary may have been 

 the case during the lied Crag Period. 



My friend Mr. Joseph Lomas, E.G.S., to whose researches, 

 with those of Prof. Herduian and his colleagues of the Liverpool 

 Biological Society, on the ' Floor-deposits of the Irish Sea,' students 

 of the Crag owe so much, has very kindly undertaken the micro- 

 scopical and chemical examination of material taken from different 

 parts of the Red Crag and Norwich Crag areas, a task involving 

 much labour and skill, for which, and for the lleport appended to 

 this paper (p. 738), my best thanks are due. His researches, 

 showing that the sandy material of the different zones of the Ped 

 Crag, and to a great extent that of the Norwich Crag also, is 

 identical in composition throughout, except that the latter contains 

 more mica, as was previously known, tends to establish the genera- 

 lization that all these beds were deposited generally (except as 

 explained on p. 735) under similar geographical conditions. 



It is interesting to notice that many of the minerals which 

 Mr. Lomas has found in the Crag sands, such as garnet, rutile, 

 zircon, tourmaline, ilmenite, and others, are common in the Tertiary 

 deposits of Belgium, 2 having been derived, according to M. Eutot, 

 from Cambrian rocks in the Ardennes, in which, he says, garnets 

 in small crystals are especially abundant. 



1 ' Littoral Drift: in its Eelation to the Outfalls of Bivers, &c.' Proc. Inst. 

 Civ. Eng. vol. exxv (1896) pp. 2-32. 



2 The occurrence of these minerals is, however, very widespread. 



