494 Horace B. Woodward — The Challii/ Boulder-clay. 



clays. Such examples I have seen at Surlingham, near Norwich, 

 and at Claydon, near Ipswich, and Mr. J. E. Marr has figured strata 

 at Sudbury that exhibit the same phenomena.-' In some cases, 

 perbaps, the basal portion of the ice carrying detritus was locally 

 arrested, while higher portions of the ice moved onwards. The 

 subsequent melting of this arrested ice led to an irregular accumula- 

 tion of drift and contorted strata. In explaining the disturbed strata 

 at Sudbury, Mr. Marr remarks that the basal portions of the land-ice 

 would be compressed laterally when driven through valleys, and 

 that contortion and even small faults might then be produced in the 

 incorporated frozen strata. On the melting of the ice the Drifts 

 would arrange themselves much as they are now found. Mr. Marr 

 has also described fragments of Crag-sand which had probably been 

 torn from the parent mass when in a frozen state, and redeposited 

 without any disturbance of their bedding, 



Mr. Wbitaker, who examined the Claydon pit in 1875, then noted 

 " a mass of Boulder Clay apparently intruded beneath older beds." ^ 

 Portions of these older deposits were described by him as " much 

 like the Crag," and with this view my notes made in 1890 quite 

 agree. (See Fig. 4.) 



Fig. 4. — Section at Chalk-pit, Claydon. 



4. Soil and decalcified Bonlder-clay. 



3. Chalky Boulder-clay. 



2. Sands and gravels (Crag series), disturbed. 



1. Chalk. 



Intrusive tongues, of course, can only be inferred where there is 

 a manifest disturbance of the strata in connection with the Boulder- 

 clay so introduced, or when the Drift has been thrust into a formation 

 unquestionably of older date. The phenomena observed at Birming- 

 ham by Crosskey may here be considered. (See ante, p. 491.) 



The larger masses or " cakes " of Secondary strata that have been 

 incorporated in the Drift arouse peculiar interest. All of those found 

 in the Eastern-Midland Counties may be connected with the agent 

 which formed the Chalky Boulder-clay. 



The great masses of disturbed Chalk, and the little broken sheets 

 of the same rock with layers of flints, found in Norfolk, occur in the 

 Contorted Drift. Mr. Clement Eeid has, however, brought forward 

 good evidence to show that the disturbances, and the introduction of 



1 Geol. Mag. 1887, p. 262, Fig. 1. 



2 "Geology of Stowmarket," pp. 9, 10. 



