496 Percy F. Kendall — Glacial Geology. 



produced by the obstruction by glacier-ice of the lower part of the 

 Trent valley ; another such obstruction, it appears probable, headed 

 back the lower reaches of the Severn (upon this point I have 

 formed no definite opinion), and the area of this lake was everywhere 

 characterized in Lewis's words by a "commingling of the drift;" 

 hence the Charnwood rocks at Nottingham, the Oolitic rocks at 

 Shiffnal, the flints at Hanbury Woodend, and, perhaps, by the over- 

 flow of such a lake, the Waldheimia at Wellington. (I might add, 

 too, for Mr. Eeade's assistance in studying the problems, the Red 

 Chalk recorded by Mr. Lucy in his paper on the " Gravels of the 

 Severn, Avon, and Evenlode," and by Buckland in an earlier paper.) 

 There remains now one errant erratic to be noticed, viz the pre- 

 Cambrian rocks of the Wrekin, found by Mr. Reade " immediately 

 to the north of the Wrekin." Mr. Reade should here be a little 

 more explicit regarding his solitary piece of good evidence. What 

 pre-Cambrian rock is it ? In what sense does he use the word 

 " immediately " ? If the rock be a volcanic (Uriconian) one, then I 

 would point out that the pre-Canibrian lavas extend some distance 

 to the northward of the Wrekin ; on the other hand, the granitoid 

 rocks (Malvernian) do not occur in the Wrekin at all. When Mr. 

 Eeade answers these questions it will be time enough to decide 

 whether of the eleven cases of abnormal transport there is, or is not, 

 just one which is inexplicable on the ice-sheet hypothesis. 



If this solitary exception will really stand criticism, I still think 

 that until it is reinforced by a good many other examples in other 

 parts of the north-west it can hardly justify us in postulating the 

 submergence of about half the land area of the British Isles. I 

 would far rather call in the aid of melting snows upon the steep 

 flanks of Ercal itself than take so great a liberty with physical 

 geography to effect so small a result. 



Can Mr. Reade not recall from his twenty years' experience of the 

 Drift round Liverpool (my Drift experience is barely five years old) 

 a few, nay even one, good and authentic illustration of a S. to N. 

 transport of a boulder ? Has he never found so much as one 

 unmistakable erratic, say, for example, the Penmaenmaur Diorite, 

 or the granitic rock of Yr Eifl ? 



I now come to the consideration of the second class of evidence, viz. : 



II. The Nature and Distribution of the Molluscan Bemains found in 

 the Anglo-Welsh Drift. 



I have carefully investigated every recorded occurrence of marine 

 shells in the Drift deposits of South Britain, and I find not a single 

 exception to the rule that they lie directly in the course of ice 

 which, by all the physical indications such as strias, transport of 

 boulders, and the like, can be shown to have come in upon the land 

 from seaward. 



It follows from this that all shelly drift should contain what may 

 be called "transmarine" erratics. Two cases were recorded where 

 there was a default of evidence on this point or an explicit declara- 

 tion of their absence. In the first case (Gloppa) foreign stones had 



