80 Mr. Lyell on a recent Formation of 



the scarcity of limestone. That substance has been the object of careful 

 search for agricultural uses ; but the only situations in which it has hitherto 

 been discovered are ; 1st, in the districts of gneiss and mica-slate, where it 

 forms some insulated masses : 2dly, in the inferior sandstone and shale, where 

 it is, however, of much rarer occurrence : 3dly, in the old red-sandstone, 

 where it appears forming a thin bed of cornstone* : lastly, as constituting the 

 limestone of the Boddin near Montrose, which contains for the most part a 

 small proportion of magnesia, and must either be considered as one of the 

 lowest of the coal-measures, lying unconformably on the inferior sandstone 

 series, or perhaps as belonging to the new red-sandf=tone formation. Lime, how- 

 ever, enters pretty extensively as an ingredient into the rocks of the two sand- 

 stone formations in which marl-lakes occur ; both the old red and the inferior 

 sandstone, as well as some of the trap-rocks which interrupt the regularity of 

 the latter, containing a notable proportion of carbonate of lime. The rock 

 seen on the surface in situ the nearest to the Bakie is the freestone of Linder- 

 tis, about a mile distant. It is a red-sandstone, slightly conglomeritic, contain- 

 ing a small proportion of carbonate of lime. 



Concerning the water of the Bakie, I have already stated that no stream 

 enters the lake ; but it is fed by numerous springs, which burst up from the 

 bottom in different parts, and are probably deep-sited, as they never fail in the 

 longest droughts. I am indebted to Dr. Daubeny, Prof. Chem. Ox., for an 

 examination of the water of the principal spring, which he finds remarkably 

 pure and exempt from mineral contents, and in no way justifying the reputa- 

 tion it has acquired of possessing medicinal qualities. The specific gravity 

 exceeds that of distilled water by less than -g-u-oth part, and when evaporated 

 in an exhausted receiver it bears only ^ „■„ „ .th of residuum. This residuum 

 consists chiefly of dark-coloured vegetable matter ; but it must also contain 

 lime, since oxalate of ammonia renders the water turbid. The presence of car- 

 bonic acid is very evident. 



It appears probable, therefore, that when the lake existed as such, the 

 springs were the medium through which a continued supply of lime was se- 

 cured for the perpetual growth and renewal of the testacea. The Charas and 

 other water-plants which are known to contain lime, are probably the instru- 



* At Reedie, not 3 miles distant north from (he Bakie, a bed of cornstone was once worked 

 for lime, but it was soon exhausted. This bed does not pass under the Bakie, but dips from 

 it, towards the Grampians, being to the south of the anticlinal line of the trough of Strathmore. 

 In the eastern part of the county, the basset-edges of a similar bed may be traced for many miles, 

 running north-east and south-west from Balmaqueen and Stracathro to Careston, where they 

 nearly thin out. The cornstone of Reedie is on the continuation of the same line. 



