But, if we are to study the Palaeolithic Age intelligently, we must endeavour to test for ourselves the dogma that Britain was then continental. That dogma has recently been questioned by geologists who have minutely re-examined in the field the phenomena of the Glacial Epoch. Mr. Clement Reid, for instance, holds that in the Palaeolithic Age England never rose more than seventy feet above its present level,[36] and that men first entered it across a narrow strait which was formed in the earlier period of glaciation.[37] It is certain that the sea then washed the coast of Sussex and the western counties; for near Selsea there is a patch of boulder-clay--the only one south of the Thames--which must have been deposited by shore-ice, and there are rocks belonging to Bognor or the Isle of Wight, to the Channel Islands, and to Brittany, which were transported by icebergs and dropped when they melted under the summer sun.[38] Again, before the first English boulder-clay was formed Arctic plants flourished near Cromer; and, says Mr. Reid,[39] ‘as these occur just above the present sea-level, and lie evenly on the strata below without deeply channelling them, the height of the land at the commencement of the Glacial Epoch, in Norfolk at any rate, must have been almost the same as it is now’. The same observer assures us that in Southern Britain the first intense cold was succeeded, after an interval of which geology has nothing to tell, by an interglacial period in which the land sunk about one hundred and forty feet below its present level, so that shingle was deposited on what is now Portsdown Hill;[40] and that it then gradually rose until, long before the second glaciation began, its level, marked by fresh-water and estuarine deposits, once more virtually coincided with the present line.[41] But, he tells us, at some time after the disappearance of the ice which deposited the latest boulder-clay of Norfolk the land stood rather higher than now;[42] and he holds that even in the early part of the Neolithic Age Britain must have been almost connected with the Continent, for many of the river valleys were excavated to depths of from sixty to seventy feet below the present level of the sea.[43] The submerged forests of Devonshire, Cornwall, and the Bristol Channel, which contain traces of neolithic handiwork, flourished at a time when the land stood from fifty to seventy feet above its present elevation.[44]