Upper Part uf the Silurian Simfem. 51 



lected by myself, but the proportion of bases to tlie acid was 

 much greater. The proportion of the lime to the acid I found 

 to be about 1-15, and that of the magnesia 1-90, while Pro- 

 fessor Croft's determination gave about 1-6, and one to 115, 

 respectively. That collected in 1845 is a nearly saturated 

 solution of gypsum, while that of 1847 contains no more than 

 about 7 pai-ts in 10,000. 



These facts indicate a rapid change in the constitution of 

 the spi'ing, and its situation shew.s it to be of comparatively 

 recent origin ; for although the powerful acid has destroyed 

 all traces of vegetation for a distance of several yards around 

 the source, the water issues from beneath the roots of an 

 enormous pine-tree, whose decayed stump still stands several 

 feet in height, while the crumbling mould, from its slow decay, 

 forms the surface soil for some distance around. Without 

 overlooking the antiseptic vii'tues of the mineral substances 

 contained in this remarkable spring, this fact shews that its 

 antiquity can scarcely be greater than a century, if indeed 

 half that cycle may not extend beyond the time of its first 

 development, while the rapid decrease in the quantity of the 

 saline bases shew that its character remains constant scarcely 

 for a twelvemonth. It should have been observed, that 

 there are four or five basins within the distance of as many 

 yards, and that they are situated on the summit of a low 

 mound, which rises with a gradual slope from the marshy 

 plain. 



The probable cause of these changes will be seen by ad- 

 verting to the character of the gypsum deposits of this for- 

 mation, which I regard as having an intimate connection with 

 this class of springs. The investigations of Mr Hall, in 

 New York, and Mr Murray, in Canada, unite in shewing that 

 the gypsum of these rocks always occurs in hillocks or dome- 

 shaped masses, varying in size from one foot to 300 or 400 

 feet in diameter, and always near the surface of the formation. 

 Sections of these masses shew them resting upon undisturbed 

 strata of limestone, while the superior strata are thrown up 

 and rest upon the flanks of the intruded hillock, often very 

 much broken, and, as Mr Hall has remarked, in part con- 

 sumed, so that one is at a loss to account for the disappearance 



