30 REPORT 1844. 



creased. A sample of genuine tobacco, by careful manipulation, affords 50 per cent, 

 of soluble matter, and when another portion of the same tobacco has been mixed with 

 15 per cent, of soluble matter, the sophisticated article can contain only 85 per cent, 

 of tobacco ; and it would be found by experiment to afford to water 57-5 of soluble, 

 and 42-5 of insoluble matter, thus affording proportions for calculating the actual 

 amount of adulteration introduced. 



On the Limestones of Yorkshire. By W. Lucas. 



The limestones may be comprised under the four following classes, viz. — 



1. The Mountain Limestone. 



2. The Magnesian Limestone, including both the upper and lower beds. 



3. The Oolitic Limestone. 



4. The Chalk. 



1. The Mountain Limestone is developed to a great extent in the district of Craven 

 and in other parts of the north and north-west portions of the county. It is of a dark 

 gray colour, and hard, breaking with a species of conchoidal fracture. Its specific 

 gravity is about 1-70. According to analysis, the following are its principal consti- 

 tuents, viz. — 



Carbonic acid 43*00 



Lime 55*50 



Foreign matter 1-50 



100-00 

 It thus appears to contain about 98*50 per cent, of carbonate of lime, and conse- 

 quently would appear to be an excellent limestone for the purposes of agriculture. 



2. The Magnesiaji Limestone. — The lower portion of this formation is found in im- 

 mediate succession to the coal measures. It is of a yellowish-white colour, and breaks 

 with a dull earthy fracture. Its specific gravity is about 2*64. 



A specimen from Conisbrough, near Doucaster, gave the following as its chief con- 

 stituent ingredients, viz. — 



Carbonic acid 46*30 



Lime 35*00 



Magnesia 17*75 



Red oxide of iron 0*75 



Insoluble matter 



100*00 

 Another specimen from the village of Weldon, adjoining the York and North Mid- 

 land Railway, near Castleford, gave the following as its principal ingredients, viz. — 



Carbonic acid 46-00 



Lime 3504 



Magnesia 17-50 



Red oxide of iron 0-90 



Insoluble matter 0*50 



Loss 006 



100-00 

 This limestone appears then to consist of 6232 per cent, carbonate of lime, and 

 36-73 carbonate of magnesia, or approaching nearly to the constitution of dolomite, 

 containing one atom carbonate of lime and one carbonate of magnesia. 



From the above statement, it would appear that this species of limestone is not well 

 calculated for agricultural purposes, except perhaps under peculiar circumstances, and 

 applied ia small quantities. 



The upper magnesian limestone is in almost immediate succession to the lower one, 

 and directly beneath the new red sandstone. It is found in considerable abundance at 

 Knottingley and Brotherton, and in other localities in this county. Its specific gra- 

 vity is about 2-64. It is of a grayish-brown colour, and much harder than the pre- 

 ceding variety. 



