MINERALS. 



canescens, Physcia ciliaris, Cladonia pyxidata, and Pertu- 

 saria communis. 



Books which may be consulted: 'History of British 

 Lichens/ W. L. Lindsay, M.D. ; ' Lichenes Britannici,' 

 Crombie ; ' The Lichen Flora of Great Britain and Ireland/ 

 Rev. W. A. Leighton. 



MINERALS. Of late years much has been discovered in 

 the mineral kingdom by the aid of the microscope, but 

 owing to the nature of the substances to be examined, 

 much preparatory work has to be done ere a satisfactory 

 examination can be made. Sections have to be cut and 

 semi-polished ere the structure can be well made out, and 

 this will be described in our next chapter. Barbadoes rock 

 showing Polycistina in situ, oolitic and nummulitic lime- 

 stone, slags from iron and copper furnaces, fossil wood, 



FIG. 138. 



minerals used in smelting, basalt, boiler incrustations, coal, 

 shale, lava, and many other minerals, furnish instructive 

 objects, and may be collected in plenty in the proper 

 localities. 



A section of porphyrine is shown in Fig. 138, which 



