°29l 
matter in these stones ; never as much as five parts 
in 100 ; but such limestones make very good lime. 
The carbonaceous matter can do no injury to the 
land, and may, under certain circumstances, be- 
come a food of the plant, as is evident from what 
was stated in the last Lecture. 
The subject of the application of the magnesian 
limestone is one of great interest. 
It had been long known to farmers in the neigh- 
bourhood of Doncaster, that lime made from a 
certain limestone applied to the land, often injured 
the crops considerably, as I mentioned in the In- 
troductory Lecture. Mr* Tennant, in making a 
series of experiments upon this peculiar calcareous 
substance, found that it contained magnesia ; and 
on mixing some calcined magnesia with soil, in 
which he sowed different seeds, he found that 
they either died, or vegetated in a very imperfect 
manner, and the plants were never healthy. And 
with great justice and ingenuity he referred the 
bad effects of the peculiar limestone to the mag- 
nesian earth it contains. 
In making some enquiries concerning this sub- 
ject, I found that there were cases in which this 
magnesian limestone was used with good effect. 
Amongst some specimens of limestone which 
Lord Somerville put into my hands, two marked as 
peculiarly good proved to be magnesian limestones. 
And lime made from the Breedon limestone is used 
in Leicestershire, where it is called hot lime ; and 
I have been informed by farmers in the neighbour- 
hood of the quarry, that they employ it advantage- 
ously in small quantities, seldom more than 25 or 
u 2 
