Chap. IV. 1.] metamorphic rocks. 57 



one case, and dull in the other. The vegetation on the two kinds of 

 rock is also peculiar^ a thorny jungle growing for the most part along 

 these stony paths (for they are used as such), while on either side of them 

 are barren sandy fields. When the beds cross the Madura road, they 

 may easily be distinguished, for white ruts have been worn across them 

 by the wheels of the passing carts, whereas no such marks have been 

 made on the harder gneiss adjoining. 



c. The Magnetie Iron Beds. — Of the many rock varieties consti- 

 tuting together the great gneissic or metamorphic (or azoic) region 

 forming the main mass of the southern part of Peninsular India, none 

 are more striking in appearance, or more important as a source of 

 mineral wealth, than the splendid beds of magnetic iron ore (Oxydu- 

 lous Iron or Magnetite of mineralogists), which are dispersed over 

 the western half of the gneissic region described in this report. To the 

 Geologist they are further of great interest and value, as they, more than 

 any of the other strata, enable him to decipher the great contortions and 

 flexures which have tended in great measure to produce the existing 

 form of surface in these regions. The number of these beds met with 

 during the progress of the survey is so considerable, and they resemble 

 each other so much in their main features, that it would be unnecessary 

 to give a separate account of each individual bed; but a list showing 

 their position, extent, and relation, may not be out of place, while a detailed 

 description of two or three of the richest and most remarkable will be 

 sufficient for all practical purposes. The list given must not, however, be 

 considered as an exhaustive one, for many of the beds in question are 

 known to extend far beyond the limits of our area, especially to the north- 

 ward. These wiU form the subject of investigation as the survey is 

 extended over the northern parts of the Salem and South Ai'cot districts. 

 How far they may extend to the west and south has also to be ascertained. 

 A brief notice of one of the most important series of these beds lying 

 near to Salem, but just beyond the western limit of our ai-ea, the well 

 H (279) 



