SCIENTIFIC SUMMARY. 
87 
earth’s surface becomes strongly marked, this profile includes an abrupt 
central line, joining at its extremities with two gently-inclined lines ; of the 
two angles thus formed that which has its apex outward constitutes the 
crest of a mountain-relief, while the other forms the ridge of a marine 
depression. In this way, at the moment when a great shore-line is con- 
stituted, it is marked on the one hand by a projecting chain, the origin of a 
continent, and on the other by a deep fosse, in which the sea collects ; the 
projecting chain moreover may only emerge in part.’ These correlated 
elevations and depressions are considered by M. de Lapparent to be due to 
foldings in the comparatively thin crust of the earth caused by the con- 
traction of its fluid nucleus. M. de Lapparent’s article contains many 
remarks of interest to geologists upon various matters more or less connected 
with, or explained by his view of the origin of mountains, and it will well 
repay careful perusal. He summarizes his results as follows : — 1 All the in- 
equalities of the surface of the globe have a single cause, which is incessantly 
in action, although it must probably manifest itself only at intervals, namely, 
the contraction of the fluid nucleus in losing its heat, whence proceeds, 
for the solid envelope, the necessity of adapting itself continually to the new 
form imposed upon it by the conditions of its equilibrium. It is thus that, 
since the earliest ages of the globe, the continents have been formed by 
successive additions, which gradually rendered their contour more and more 
complicated. The surface of the sea has constantly diminished in extent, 
but at the same time its depth has constantly increased with the elevation of 
the continents. Hence have arisen those diverse physical conditions, in 
which the natural effects of latitude are complicated by a thousand modifi- 
cations due to the nature of the soil, to altitude, to exposure, to vicinity to, or 
distance from, the sea. Thus all those external conditions, the variety of 
which gives so great a charm to our globe, at the same time that it is the 
most powerful of stimulants to human activity, are contained in their germ 
in the law that we have laid down.’ 
Chalk Flints . — At the last meeting of the Geological Society (December 
19th), Dr. Wallich read a contribution towards the solution of that qucestio 
vexata, the origin and mode of formation of the flints which occur so abun- 
dantly in certain parts of the Cretaceous series. Taking as the basis of his 
conclusions the fact brought to notice by him in 1860, namely, that the 
whole of the Protozoan life at the sea-bed is strictly limited to the immediate 
surface-layer of the muddy deposits, he pointed out in detail the successive 
stages of the flint-formation, from the period when the chief portion of the 
silica of which they are composed was eliminated from the ocean-water by 
the deep-sea sponges, to the period when it became consolidated in layers or 
sheets conforming to the stratification of the Chalk. In relation to this 
subject the author claims to have sustained the following conclusions : — 
1. That the silica of the flints is derived mainly from the sponge-beds and 
sponge-fields, which exist in immense profusion over the areas occupied by 
the Globigerine or calcareous ‘ ooze.’ 2. That the deep-sea sponges, with 
their environment of protoplasmic matter, constitute by far the most impor- 
tant and essential factors in the production and stratification of the flints, 
j 3. That whereas nearly the whole of the carbonate of lime, derived partly 
from Foraminifera and other organisms that have lived and died at the 
