343 



same slope that nature always adopts in her arrangement 

 of particles of earth on the hill-sides, which is at an angle 

 something less than forty-five degrees with the horizon : it 

 then remains in a quiet state until the surface is completely 

 covered over by shrubs and herbaceous plants, which are 

 perfectly competent, by the ramifying entanglement of 

 their rootlets, to secure permanently the banks from all 

 further encroachments. Whenever [the angle is of any 

 greater degree, these slides must invariably take place. 



The calcareous concretions embraced in the clays of this 

 formation present a very singular feature in their construc- 

 tion. They are exceedingly common among some of its 

 strata ; and from the peculiar variability of their forms, 

 it becomes very difficult to conceive any method by which 

 to communicate a definite idea of their remarkable ap- 

 pearances, other than by a reference to the specimens 

 themselves. They are always limited to the upper por- 

 tion of the deposit, or that part most commonly selected 

 for the manufacturing of brick. From the size, color, and 

 then' geological position amid the clays, they will easily 

 admit of a separation into two distinct varieties : the first, 

 or smaller of these, are most generally of a light yellow- 

 ish color, about an inch or an inch and a half in their 

 diameters, and are exclusively confined to the divisional 

 seams of sand in the upper or disruptured portion of the 

 series. The second and larger variety, as far as observa- 

 tion has hitherto extended, appears to be restricted to a 

 single stratum of the middle, or variegated portion of the 

 clays near to its upper termination, and situated about 

 four feet from its junction with the overlying or distui-b- 

 ed member of the deposit: they are for the most part 

 about three or four inches in diameter, with a length fre- 

 quently of more than a yard, and of a deep stone-blue 

 color. Both of these varieties sometimes present the same 

 peculiarities of form, but they differ considerably in their 

 chemical analysis. 



