INTRODUCTION. 



and Severn Canal, which is called '^ Thames-liead bi-idge; " but that 

 which is to be regarded as the true head of the Thames is about three 

 or four miles south of Cheltenham. Two streams rise, one from 

 fourteen springs at what is popularly called the Seven Wells, and 

 the other from four springs near Ullen Farm, the westernmost of 

 which springs is the real (i.e. the remotest) head of the river : both 

 streams rise on the south-eastern slope of the Cotswolds, and 

 form by their junction, about a mile from their respective sources, the 

 river Churn, a name the element of which is embodied in the ancient 

 name Oorinium, and modern name Cirencester, of the town by which 

 it flows, and in the name of two villages, North and South Cerney, 

 which are near it. At CricMade, nineteen to twenty miles from its 

 source, the Churn joins the commonly reputed Isis or Thames, the 

 length of which above the junction is only about ten to eleven miles.' 



Mr. Bravender remarks {Proceedings of Cotsivold Club, 1867) that, 

 according to the Ordnance map, the Thames commences in Wiltshire, 

 at a place called Waterhay Bridge, about a mile below Ashton 

 Keynes, and about 3 miles west of Cricklade. Above this point 

 it is called Swillbrook, and is joined by the brook running from the 

 spring in Trewsbury Mead near Cirencester, mentioned above. 



The whole length of the Thames is 201 miles, and the portion of 

 it bounding Middlesex is about 45 miles long, following a serpentine 

 course from Staines to Blackwall. 



The tide ascends to Teddington about 18 miles above London 

 Bridge, and the following species, partial to brackish water, occur in 

 Middlesex : some, however, are now no longer to be found so high : — 



