The rivers flow mainly in a westerly or north-westerly direction. Spreading evenly over the plain in almost parallel lines, they serve to drain and fertilize the land, which thus affords the finest pasturage for cattle. Dairy-farming and stock-raising have therefore become the principal occupation of the inhabitants of the Cheshire midlands; and on market days the piles of the famous Cheshire cheese are generally the first thing we notice in the open market-places of our country towns. The most noticeable feature of the county are the two estuaries of the Dee and the Mersey. The tract enclosed between them is for the most part flat, Heswall Hill, the highest point, being little more than 300 feet in height, and the lowest parts have to be protected from the inroads of the sea by long embankments. Several portions were in fact, at one time separated from the mainland, like Hilbre Isle at the present day, as is shown by the names Wallasey, 'isle of the Welsh or strangers,' and Ince 'an island'. In the Middle Ages, owing to the importance of Chester, the Dee was the principal outlet for the trade of the north-west, as Bristol was for the south-west of England. In those days Liverpool was but an insignificant town, and the Mersey was known as the 'Creek of Chester'. But in the fourteenth and fifteenth centuries the shipping trade of the Dee declined owing to the great accumulation of sand and silt in the channel. When vessels could no longer unload or ship their merchandise under the walls of Chester a quay was formed at Shotwick, some six miles along the northern shore of the estuary. In this neighbourhood over two thousand acres of land have been recovered from the sea that once flowed over them. Navigation was partially restored as far as Chester for small vessels by a new artificial channel, but since the rise of the cotton and other great industries in South Lancashire Liverpool and Birkenhead have replaced Chester and become the second port in the kingdom. Cheshire also possesses a miniature 'Lake District'. Between the Bollin and the Weaver are scattered many lakelets or 'meres'. They are particularly numerous in the salt districts, where they are due to the pumping of brine which has been going on for ages, and caused the sinking down of the overlying rocks. In the neighbourhood of Northwich the sheets of water thus formed are called 'flashes'.