Clement Reid — On Bust and Soils. 165 



In Mr. C. D. Walcott's admirable paper on "The Trilobite, New 

 and Old Evidence relating to its Organization," (Bulletin of the 

 Museum of Comparative Zoology at Harvard College, vol. viii. No. 

 10, Cambridge, 1881), in his restoration of the ventral surface of 

 Calymene senaria, plate vi. fig. 1, he gives 26 pairs of appendages, 

 all, with the exception of the posterior cephalic pair, of a similar 

 simple cylindrical 7-jointed structure, and extending to the extremity 

 of the pygidium. Assuming this restoration to be more or less con- 

 jectural, we venture to suggest that the last seven pairs, belonging 

 to the pygidium, were more probably lamelliform branchigerous 

 appendages, as in Limulus and in living Isopods. — H. W. 



IV. — Dust and Soils. 



By Clement Eeid, F.G.S., 

 of the Geological Survey of England and "Wales. 



IN Darwin's recently published work on vegetable mould, allusion 

 is made to the fact that " In countries where the summer is 

 long and dry, the mould in protected places must be largely increased 

 by dust blown from other and more exposed places." A few lines 

 further on, however, he states that " In humid countries like Great 

 Britain, as long as the land remains in its natural state clothed with 

 vegetation, the mould in any one place can hardly be much increased 

 by dust." ^ To this statement no exception can be taken, if we 

 remember that it only applies to a period when the climate is humid, 

 and to a country clothed tuith vegetation. 



Nearly all writers on the surface geology of England and Western 

 Europe speak of the connection between the soil and subsoil as most 

 intimate, the soil being normally formed from the weathering of the 

 subsoil. Taking a manual which is considered a standard authority 

 on the subject, we find the following: — "The general result of this 

 comparison has been, that in almost every country the soils, as a 

 whole, have a resemblance to the rocks beneath them, similar to that 

 which the loose earth derived from the crumbling of a rock before 

 our eyes bears to the rock of which it lately formed a part. The 

 conclusion, therefore, is irresistible, that soils, generally speaking, 

 have been formed by the crumbling or decay of the solid rocks. 



. . . . The cause of the diversity of soils in different districts, 

 therefore, is no longer obscure. If the subjacent rocks in two 

 localities differ, the soils met with there are likely to differ also, and 

 in an equal degree." ^ 



Were it correct that the character of the soil can be known from 

 the nature of the underlying rock, we might accept without hesita- 

 tion the above rather sweeping statement. But unfortunately soils 



' Darwin, The Formation of Vegetable Mould through the Action of "Worms, pp. 

 236, 237. 



2 Johnston and Cameron, Elements of Agricultural Chemistry and Geology, 

 13th edition, p. 90. 



