Page:Transactions of the Natural History Society of Northumberland, Durham, and Newcastle-upon-Tyne (1867).djvu/90

72 expected. The greatest concentration of these boreal plants is, we see, in the most southern of the districts. The special richness of Teesdale in Montane species is a fact which we cannot undertake to explain; but if the relative abundance with which these plants occur in the different districts were to be taken into consideration, the contrast would be much more striking than it is now. The small proportion of the total number of species which any other district, except that of the Tees, yields is noteworthy, especially the lowness of the figure for district number one, which, besides being the most northern in position, contains the high Cheviot peaks, and a wide area of elevated ground. We may take the even distribution of a considerable number of these plants through the districts as indicating (what is a characteristic feature of the physical geography of the two counties) the large extent of surface which is occupied by low hilly country, a circumstance which explains also a point upon which we shall afterwards have occasion to dwell, and the large number of plants common in the south and centre of England that come to a stop in their wanderings towards the north within our bounds. So much premised by way of introduction, we will now take the districts seriatim.

The Tweed altogether drains an area of 1870 square miles, including nearly the whole of Roxburghshire, Berwickshire, Peeblesshire, and Selkirkshire, and portions of Haddingtonshire, Edinburghshire, Lanarkshire, and Northumberland. At the town of Peebles, 50 miles from the coast in a direct line, it is only 500 feet above sea-level in altitude. For about 18 miles in a direct line the main branch forms the northern boundary of Northumberland, a broad sinuous stream, flowing more rapidly than is usual with rivers of so large a size, past Carham, Cornhill, Tillmouth, Twizell, and the ruined castle of Norham to Berwick. The banks are in some places level and grassy, but sometimes steep and wooded. The influence of the tide reaches up to Norham, which is 10 miles inland. There is a small burn