138 



separately. Rocks of secondary formation are va- 

 rious, but I shall only take notice of such as contain 

 organick remains ; such as secondary or shell lime- 

 stone, containing various species of shell-fish and other 

 animals, completely changed in their nature, and, by 

 being combined with carbonate of lime, formed into a 

 compact or solid mass, and susceptible of being wrought 

 into various shapes or forms, and of being converted to 

 sundry useful purposes. 



Also, secondary gypsum, containing impressions of 

 a variety of fishes > and animals ; likewise, seconda- 

 ry slate, containing perfect impressions of fishes and of 

 various vegetable substances, which, though changed 

 in substance, have suffered no change in form. 



In these several rocks are often found different mi- 

 neral substances, such as lead, zinc, &c. 



The alluvial formation is generally composed of 

 sand, gravel, and rolled pebbles of different kinds. 



In this formation, notwithstanding its being, as I 

 have observed, the result of an accidental operation, 

 we likewise see the mineralizing powers exerted, 

 though in a far weaker degree, and the process of new 

 formations carried on, though upon a much smaller 

 scale, and to a far less extent. 



In this formation, we find beds of bituminous wood, 

 and coal ; petrified wood ; immense beds of variously 

 coloured clays ; extensive mines or beds of fine argil- 

 laceous, and bog iron ores ; beautiful crystals of sele- 

 nite, &c. These and many other substances are found 

 in place in various parts of the great alluvial district, 



