1867.] WOOD SOUTH-EAST OF ENGLAND. 417 



Nothing, however, is clearer from the whole map than that the valley itself had 

 no existence whatever at the period of the Glacial clay. In the case of the 

 Blackwater, Mr. Dawkins refers me to the Boulder-clay of Ingatestone, Butts- 

 bury, and Mountnessing. These places are more than ten miles from the nearest 

 edge of the Blackwater valley ! and they form the heights out of which the valley 

 of the Wid, a tributary of the Chelmer, is cut. They are shown in my Survey- 

 map to occur in a country affected by the structure shown in figs. 1-3. Had the 

 Boulder-clay shown in the centre of the section fig. 9, however, been referred to, 

 there would have been some colour for the assertion ; but I trust that the structure 

 shown in that section has been sufficiently explained to prove that the Grlacial 

 clay in the trough of arc 3 does not owe its position to any Preglacial existence 

 of the Blackwater valley, which for a few miles of its course has incorporated 

 into itself a part of arc 3, just as does the Koding, for some two miles, at 

 Navestock incorporate a part of one of the depressions illustrated by figs. 1-3. 

 In the case of the Colne valley, Mr. Dawkins tells me that the Boulder-clay 

 " occupies a very large area in it, and can be seen in the valley near Colchester, 

 immediately opposite Lexden." To this, all that I need say is, that I can find 

 nothing of the sort there. The valley of the Colne (which is free from all com- 

 plexity of structure) is, opposite Lexden, and near Colchester, occupied in its 

 base by the London clay, the sides being formed by the Middle Q-lacial gravel, 

 while the Boulder-clay occupies the more distant plateau-country, this valley being 

 simply excavated in a plateau of Upper and Middle Glacial deposits. 



Having for several years made it a special object to examine the structure of 

 these valleys, I do not hesitate to affirm in the most unqualified manner that not 

 only these three river-valleys, but every other in the south-east of England to 

 which the Upper and Middle Glacial deposits occur sufficiently near to afford 

 positive evidence upon the question, have been formed subsequently to the 

 Upper Glacial clay. The exceptions alluded to in a previous note (page 415) 

 refer not to river-valleys^ but only to some dry depressions. But while that is 

 so, it is of the utmost importance to bear in mind that there are Boulder- 

 clays in the East of England of true valley or Postglacial origin, and depo- 

 sited after the excavation of the valleys through the Upper Glacial clay. Of 

 this, one instance affecting the Yare valley is given by Mr. Harmer, in the 23rd 

 volume of the Journal ; and he informs me that he has found the same thing 

 in the valleys of the Gipping, in Suffolk, and Tese and Chet, in Norfolk ; and I 

 hope, in conjunction with another Fellow of the Society, shortly to lay before it 

 evidence of a similar Postglacial or valley Boulder-clay spreading over hundreds 

 of square miles and wrapping the denuded edges of the Upper Glacial clay like 

 a cloth. 



