32 The Origin of the 



dikes of trap; as may be seen at Port-na- Cross, on 

 the coast of Ayrshire, near West Kilbride, and at 

 other places. 



The more delicate marking of the grain of wood 

 on the surface of these Cairo specimens is to be 

 ascribed to the finer grain of the sand in which the 

 wood had lain, and to the greater fluidity of the 

 molten silex which fell and ran along the ground. 

 This may be illustrated by the analogy of the case 

 of flowing lava, of which I take a statement from 

 De la Beche. 2 "The following," says he, "is a 

 summary from various authorities of the heat and 

 appearance of a lava current. Lava, when observed 

 as near as possible to the point from whence it 

 issues, is, for the most part, a semifluid mass of the 

 consistency of honey, but sometimes so liquid as to 

 penetrate the fibre of wood. It soon cools externally, 

 and therefore exhibits a rough unequal surface ; but 

 as it is a bad conductor of heat, the internal mass 

 remains liquid long after the portion exposed to the 

 air has become solidified.' " 



To these arguments of a meteoric origin of the 

 chalk and flint formation I may add the evidence 

 furnished by some specimens of yet a different kind. 

 The spherical form, as has been remarked, may 

 become ellipsoidal from more rapid motion in space ; 

 and in some cases the ellipsoidal form has become 

 very remarkably elongated, as if by violent pro- 

 jection, like an arrowy missile. The psalmist 

 perhaps alludes to these in connection with a 

 memorable meteoric storm — probably that which 



destruction "by burning ; showing how it was traditionally regarded 

 as a naming downpour of fire, £evois verois, " a new kind of rain, 

 and hail, and inexorable showers." 

 2 "Manual of Geology," pp. 107, 108. 



