AVOOD AND ROME LINCOLNSHIRE AND S.E. YORKSHIRE. 167 



excavations at Hull we ourselves examined ; and they showed the 

 Hessle clay (underlain by the sand d, and that again by the purple 

 clay) irregularly denuded and overlain by a bed of silt upwards of 

 20 feet thick, at the bottom of which were the remains of a forest 

 growing upon, and with the stools in places rooted into, the Hessle 

 clay *. "This deep accumulation of silt abounded to the very bottom 

 (where the shells rested on the forest) with the ordinary estuarine 

 mollusca of the Humber — Scrobicularia piperata, Tellina solidula. 

 Cardium edule, Littorina littorea, &c. In part this forest-bed was 

 also underlain by the silt, showing an oscillation of level during its 

 growth. We have in this the most unequivocal evidence of a very 

 recent subsidence in an easterly direction, by which the Humber 

 has been introduced over a previous, though still a late, Postglacial 

 land surface. This silt seems to be the same deposit which occupies 

 all the lowest grounds around the Humber and along the north 

 Lincolnshire coast, and is easily distinguishable, by the dark colour 

 and fertility of its soil, from the foxy and less fertile Hessle-clay 

 tracts which it fringes ; and this again seems to indicate some oscil- 

 lation of level since the depression which submerged the forest, 

 because much of this silt (or often blackish clay) deposit is above 

 high-water mark. At Hull the dock-borings showed this forest to 

 be now from 20 to 37 feet below high-water mark of ordinaiy 

 spring tides, the whole of that depth being occupied by the silt with 

 moUusca and salt water. The borings for the Grimsby Docks dis- 

 closed the same forest-bed at still greater depths, varying from 35 

 to 52 feet below high water of ordinary spring tides, and every- 

 where covered with silt and salt water. Prom the Grimsby borings 

 (which were more than 100 in number, and principally carried to 

 depths of from 70 to 80, but in some to upwards of 100 feet below high 

 water) regular sections were constructed by the dock-engineers. 

 An examination of these has satisfied us that the lower part of the 

 purple clay, which, with a thickness varying from 20 to 50 feet (in- 

 clusive of the sand- and gravel-beds c' and b), rests immediately on the 

 chalk, is here cut through by a trough containing sands and gravels 

 of the series / before described. These being in places covered by 

 the forest-bed, the depression which has submerged the land surface 

 would appear to have been posterior to the formation of the beds /. 

 In some parts there were two forest-surfaces, divided by a bed of 

 leafy clay, from 5 to 15 feet thick, but both newer than the sands 

 which we refer to series /. We are informed by the engineer, E. 

 H. Clarke, Esq., that abundance of the stems and roots of the trees 

 were found in excavating the docks. The old troughs thus filled 

 with gravel, and overspread with silt and black mud now converted 

 into land, penetrate the north-east of Lincolnshire for several 

 miles, and give rise to a common feature of this part, called blow- 

 wells. If we are right in referring these submerged troughs of 

 gravel to those marked/ and/' on the coast- section, it follows that 

 not only has there been the recent considerable easterly depression 

 so unequivocally shown by the position of the forest, but this de- 

 * See section in appendix. 



