INTRODUCTORY CHAPTER, xxvii 



and exposing common earth to the influence of the air and atmo- 

 sphere, that a pale brown soil is changed to a much darker hue. 

 We observe, that as flowers gradually open, and are exposed to the 

 air, the}' throw ofl" their old colom-, and acquire a new one ; but, 

 whether certain component parts of earth or clay, are capable of 

 being changed into any other colours than dark brown, or black, 

 by a long exposure to the sun, air and moisture, I shall leave to 

 the decision of those who are skilled in the sciences of natural 

 philosophy and chemistry.* 



I have jiow endeavoured to explain the most striking facts, 

 connected with the Geology and Mineralogy of St. Helena, which 

 have come under my personal inspection. Having done so, I 

 must here claim the indulgence of the reader, not only on account 

 of the preceding observations having been made in a casual 

 manner, but because they relate to sciences of which'I do not 

 profess to have any skill or knowledge. I should indeed have 

 contented myself with barely stating facts, and have left it to 

 more, able hands to form conclusions : but in adhering to this 

 mode, I was fearful I should have rendered the subject less in- 

 telligible. It is for this reason I have been induced, occasionally, 

 to draw conclusions, or to offer conjectures : but as these are given 

 at all times with diffidence, I beg they maybe received merely as 

 suggestions ; in which shape they may be of use to those who 



* Cronstedt is of opinion " that common clay, especially the blue, grey, and red 

 " kinds, may derive their origin from mud ; and as the mud proceeds from vegetables, it 

 " will thence follow, that the varieties of clay just mentioned, are notliing else but the 

 " common mould altered, after a length of time, by means of water." 



Some of the white clays of St. Helena appear to be a species of lithotnarga, or stone- 

 marrow, being as fat and slippery as soap. Possibly the white are the primitive clays of 

 the eastern part of the island, which have, in the course of ages, been changed into a 

 variety of colours by some unsearchable cause in nature. 



