Great Valley of the Scottish Lowlands. 109 
stone noticed by Mr Murcuison at Pontesbury, and other places 
in the Shropshire coal district; for the opinion expressed by M. 
Aeassiz, relative to the ichthyolites which have been found in 
the Scottish coal-fields, has shewn that neither the Burdiehouse 
limestone, nor any of the other beds of the carboniferous group 
in this country, with which we are at present acquainted, have 
any claim to be so considered ; nevertheless, there are peculiari- 
ties in the character of the limestone at Burdiehouse, both in re- 
gard to its organic contents, and to its position in the series, 
which render it an object of the highest geological interest: and 
the discovery by Dr H1nzERr1, of a new species of sauroid fish, the 
Megalichthys, in that limestone, is one of the most important 
that has been made in the present times. 
In Scotland, the greater part of the secondary formations, in- 
cluding the coal-measures, have been deposited in that extensive 
district which now forms the great valley of the Scottish Low- 
lands, and separates the primary country, of which the northern- 
most extremity of Great Britain is chiefly composed, from the 
transition chain of the southern border (at that time probably 
partly submarine), which may be geologically considered as. the 
South Highlands. 
According to W1Lu1ams*, a line drawn from the mouth of the 
Tay, passing through Stirling to the northern extremity of the 
Isle of Arran, and another nearly parallel to it from St Abb’s 
Head on the east coast, to Girvan on the west, will include be- 
tween them the whole of the coal-fields of Scotland, with the ex- 
ception of the insulated coal basins on the Nith and the Esk in 
Dumfriesshire, and the seams of coal that have been worked in 
Roxburghshire and on the coast of Berwickshire. The coal beds 
of Brora, and those that have been met with in some of the He- 
brides, have generally been referred to formations of a more re- 
cent period. 
* History of the Mineral Kingdom, vol. ii. p. 302. 
