DEFINITION OF THE AREA. 



Ixxi 



Lake reached at the time of its existence through the portals at 

 Perth city, between the extensions of the Sidlaw Hills on the one 

 side and those of the Ochil range on the other side of the river 

 Tay, and thence across or along the carselands of the lower Earn, 

 and so through the Vale of Menteith in Forth to Clyde; and 

 because the land now occupying that ancient lake has such a low 

 elevation above the present sea-level, — because of this it might be 

 argued that a much more extensive faunal area is thereby formed, 

 and parts of Forth and even Clyde should be included, but T 

 cannot see that any good result or real service would ensue were I 

 to follow this plan. 



In a similar way the areas of Forth and Clyde might be united, 

 and perhaps with greater justice. The altitude of the minor water- 

 sheds of Forth and Clyde reach only 120 feet between the head- 

 waters of the Bonny — tributary to Forth — and of the Kelvin of 

 Clyde drainage area, while on the north side of the Ochils and again 

 in the Vale of Menteith the altitudes are even less. But this com- 

 parison is only mentioned in passing, and with the idea of instituting 

 a comparison, and does not call for further treatment in this place. 



Keturning to the Tay area, we find that the minor range of the 

 Sidlaw Hills is only an isolated patch, both sides of which contribute 

 their drainages to the river Tay, and the extension to the eastward 

 runs out on the coast in the minor headland of the Eed Head in 

 Forfarshire, at an elevation above the tide of some 200 feet. At the 

 time of the existence of the ancient Caledonian Lake, the Sidlaw 

 Hills must have formed a true island, and at the present day they 

 cannot be held to have greatly increased in any faunal value they 

 had, but have maintained a very similar position. 



I do not pursue this part of my subject further here, because I 

 believe the definition of the Tay Basin will have become sufficiently 

 evident in the descriptive chapters already given. 



