OF MARLBOROUGH. Xlll 



such an extent during one month, that its entire descendants 

 can form a bed of silica 25 square miles in extent and 1| 

 feet thick " (Jukes's Manual of Geology). According to the 

 universal law of nature, these minute creatures are the prey 

 of most of the shell-fish, and so are not allowed to increase 

 at such an enormous rate ; but if we suppose for a moment 

 1000 of these siliceous or calcareous creatures and their 

 descendants unchecked to be scattered over 40 square miles, 

 and to be supplied with sufficient silica or lime from the 

 ocean, we see that at the end of one month we should have 

 a bed of silica or limestone more than 1000 feet thick : i. e. 

 a bed similar to, and as thick as the Upper and Lower White 

 Chalk would be formed over 40 square miles in a single 

 month. 



The formation of limestones by these minute animals is 

 intimately connected with the geology of Marlborough ; for 

 it has been found on examination that the White Chalk, 

 which is a carbonate of lime, was formed just in the same 

 way as the bed of Poraminifera or calcareous shells which 

 is now in course of formation in the Atlantic Ocean. When 

 pulverized in water and examined through a microscope, it 

 is found to consist of fragments of minute corallines and 

 perfect calcareous shells, the chambers of which are fre- 

 quently filled with thousands of other still more minute 

 shells which abound in every grain of chalk. In the same 

 way the flint has probably been obtained from the waters 

 of the ocean and turned into a solid form by the siliceous 

 animalcules, and then spread out into layers, or, as is more 

 usually the case, collected into nodules, often around a coral 

 or a sponge, by chemical agency. Chalk flints have a white 

 coating, which is often of considerable thickness, and in 

 which layers may be distinctly seen, showing the forms of 

 the successive films. It does not appear to be sufficiently 

 made out why the flint-nodules are collected in layers in 

 the chalk. It almost seems as if the shells of each set 



