THE SEVEBN TUNNEL SECTION. 83 



is very coarse compared witli the upper bods, and a short 

 distance before the thinning out of the ground, it is more 

 angular, and littlo water-worn, cleai'ly showing that it came 

 oast of the river. There are largo boulders of quartz, mill- 

 stone grit, coal-measuro sandstone, slate (probably from 

 Cumberland), Lickey pebbles, fine quartzites. Old Red 

 conglomerate, trap rocks, and rolled Lias grypliites. I found 

 one piece of glaciated dioivitc. The Drift is probably of two 

 ages. One may be considered as belonging to the low-level 

 drifts of Mr. Prestwich, in which is mixed up high-level 

 diift with rocks derived from far distant places." 



The four pill-coursca mentioned by Mr. Lucy are very i 



clearly shown in the section. They were without doubt 

 excavated in the blue marsh clay, and underlying beds sub- 

 sequent to their deposition, but are older tlian the yellow 

 surface clay which overlies them. Their symmetrical shape 

 would seem to me to indicate that they were not long 

 occupied as watercourses. 



In the Caldecot shaft (2 on the section), which was 

 sunk through the alluvium of the river ISTedden, a band of 

 Scrobicularia marl was found, 39 feet from the surface. 

 " It is of yellowish grey colour, and is characterised by an 

 admixture of fresh-water and brackish-water shells, such as 

 Limncca, Planorbis, Scrobicularia pipcrata, and Cardium edule. 

 Diatoms are common in it, and also remains of Ghara." 

 (W. J. Sollas.) 



Prof. Sollas classifies the alluvial deposits in the following 



o 



manner : — 



■ a. More sandy zone, five to seven 

 feet. 

 Zone 1. a Upper Clay. ^ b. More argillaceous zone, with 



disseminated vegetable 

 matter. 

 /3 Upper Peat. 



