MODE IX. GYPSUM. 4$ 1 



" Heavy spar* is found in the marl at Mont- 

 martre : it is more abundant in the hill of Belle- 

 ville, where it is met with in misshapen masses, 

 greyish, flattened and rounded, at ten or twelve 

 feet from the surface of the earth. 



<* The trunk of a tree agatised, which I found 

 at Montmartre in 1778, serves to support my 

 theory on the agatisation of vegetable sub- 

 stances. See page 168, vol. ii. of my Chemical 

 analysis of the three kingdoms. This agatised 

 trunk of a tree was thirty feet long, and nine 

 inches in diameter; it was rather compressed, 

 lying horizontally from north to south, and was 

 at least 100 feet from the summit of the hill, be- 

 tween the two lowest beds of gypsum, of which 

 the interior part was crystallised. The inter- 

 stices of this agatised wood are ornamented with 

 little regular rock crystals, of various colours. 

 A part of this wood is brown and compact : this 

 colour is owing to iron and oil, principles of the 

 woody substance. I have inquired, since then, 

 if any agatised wood had been found at Mont- 

 martre, and I was assured that it had not. 



" The shelly sandstone which is found at 

 Montmartre, seems of the same date with the 

 agatised wood : this sandstone contains white 



* Strontian. 



