Freshwater Limestone in Forfarshire, Sgc. 83 



been washed out of the soft marl, which itself contains but few of them. This 

 formation extends for about 100 yards along the southern border of the lake, 

 and is confined to that part which in summer is dry, and in winter lies below 

 the level of the water. 



Comparison of the Limestone of the Bakie with other Freshwater Limestones 

 both of recent and of ancient Formation. 



The limestone of the Bakie very closely resembles the tufa deposited from 

 springs, which issuing highly charged with carbonic acid or sulphuretted hy- 

 drogen from limestone strata, contain a quantity of lime in solution. Such 

 deposits are common in most calcareous districts ; but are particularly abun- 

 dant in some parts of Italy ; as, for instance, at the waterfall of Terni, and at 

 the baths of St. Philip on the frontiers of Tuscany some miles from Radico- 

 fani, and near Rome at the cascade of Tivoli and the lakes of Tartari and Sol- 

 fatarra. The tufa of the last-mentioned lake is compact, and in that respect 

 comes nearest to the ancient freshwater limestone of the same country. []Oss. 

 Foss. 2d edit. tom. ii. pp. 560, 552.] 



The modern deposit however, the most analogous to that of the Bakie, is 

 that described by M. Beudant, as daily forming underwater at Czegled and 

 other places in the great plain of Hungary. The limestone thus produced is 

 of a grayish or yellowish colour, divides naturally into slabs, and is sometimes 

 sufficiently solid to serve for building. It incloses Planorbes and other shells 

 identical with those now living in the neighbouring marshes. It is traversed 

 by irregular tubes which are perpendicular to the surfaces of the slabs ; and 

 are considered by M. Beudant as having been caused by the disengagement 

 of gas. [Voyage en Hongrie, tom. ii. p. 353, and tom. iii. p. 285.] 



Of the ancient freshwater limestones, the most similar to the rock-marl of 

 the Bakie are those of Italy. This kind of limestone, having been quarried ex- 

 tensively by the Romans near Tivoli, (Tibur,) has acquired in Italy the name 

 of Travertino (lapis Tihurtinus), a term now applied also to modern tufa and 

 to any very soft and cavernous limestone. The travertino is white when first 

 taken from the quarry ; but after a time it becomes yellowish, and at length 

 acquires that reddish hue which is so agreeable to the eye, and so much 

 heightens the architectural effect of the monuments of ancient Rome. [Breis- 

 lak. Inst. Geol. tom. ii. p. 123.] It is the material, in fact, of which not only 

 the Coliseum and many other ancient works in Rome are constructed, but also 

 the far older temples in the Grecian colony of Paestum. 



The travertino of the great quarries of Ponte Lucano, at the foot of the 

 hills of Tivoli, is described by Von Buch as lying in horizontal beds, and as 



M 2 



