456 Mr. Stark's Observations on Mr. Lyell's Paper 



soluble in acids" ; for both with hydro-chioric and acetic acids 

 it left a residuum which proved to be siHca and ahimina. 

 I notice this fact as being of importance to a theory I am 

 about to advance relative to the chalk formation. 



As to the origin of the sand-pipes, Mr. Lyell observes: 

 " We have now to consider in what manner these cylindrical 

 hollows have been first formed and then filled with gravel 

 and sand. If no pipes but those of the smallest size had oc- 

 curred, we might have imagined that the top roots of large 

 trees had first pierced the chalk, and then after growing to 

 their full size and decaying had left a vacant space into which 

 loam and gravel fell. But when we reflect on the dimensions 

 of some of the pipes, we at once perceive that more powerful 

 causes must be appealed to." 



" On consideration of all the facts we can scarcely hesitate 

 to admit the following conclusions: — That the chalk has 

 been removed by the corroding action of water charged with 

 acid, in which the siliceous nodules being insoluble were left 

 in sitti in the smaller pipes after the calcareous matrix had 

 been dissolved." 



It appears to me that all this may be satisfactorily ac- 

 counted for without presuming that the " water was charged 

 with acid." The appearance of every mass of chalk which 

 I have seen warrants our concluding that it was deposited at 

 different times from a solution or suspension in water. The 

 layers which a section of any mass of chalk exhibits on exca- 

 vation, proves that a deposit of a limited depth has taken place 

 and become partially solidijied before a super deposit had 

 commenced, and consequently there must have been a very 

 considerable lapse of time between the lowermost and the 

 uppermost stratum of chalk in any deep mass of that sub- 

 stance. We cannot hesitate to admit this, not only from 

 the evident lines (generally horizontal, but sometimes with a 

 slight dip) which every perpendicular face of chalk exhibits, 

 but also from the fact, that upon each of those lines, or rather 

 tables, are deposited dark-coloured particles, principally com- 

 posed of siliceous and argillaceous matter, as if they were 

 precipitated from an upper stratum of the calcareous mass, 

 whilst it was in a semi-fluid state, and after the under, or 

 previously deposited, stratum had been desiccated. livery 

 layer of chalk appears to me to have been thus deposited, till 

 the aggregate formed the immense calcareous masses we now 

 witness. 



Admitting this hypothesis, (and I think the facts of the case 

 warrant such an admission) there must have occurred in the 

 course of solidification considerable fissures in these deposits ; 



