12 
material, without a natural tendency to be attracted to, or 
adhere to each other, are found concreted into a dense, and 
sometimes crystallized mass. One species of rock, nummulitic 
limestone, the material of which the Egyptian Pyramids are 
built, and of great durability, consists mainly of the perfect 
shells and shields of a molluscous animal, which would cer- 
tainly have been decomposed by heat. So also would most 
minerals ascribed to igneous origin. It appears evident that 
the agent of concretion is mineralized water, probably acted 
upon in the laboratory of nature by currents of electricity, 
and thus that metals and minerals are elaborated from masses 
of earths in a tine state of comminution and water com- 
mingled, the metals concreted in veins, or nodules, and the 
minerals into their incasing rocks. Some geologists consider 
basalt as lava ; others, and earnest investigators too, regard 
it as an aqueous concretion. Its appearance in detached 
blocks in the quarry favours the latter view. The Arctic 
explorers, Dr. Kane and Sir John Richardson, both mention 
the basaltic crystalline arrangement of columns of ice. 
In the words of Dr. Brande, F. G.S., " Geology is thronged 
with records of strange and mighty changes and convulsions, 
of revolutions of climate, ... of periods when our 
present continents were at the bottom of the ocean, from 
which they seem to have been elevated sometimes by the 
slowest degrees, and at other times by a more rapid and 
violent cause. " Other geologists admit that the science dis- 
closes evidences that, times and again, while frigid, tropical, 
and temperate zones have been transposed in almost every 
part of our earth's surface, the ocean has alternately sub- 
merged and withdrawn from every quarter of the known 
world, even rising and leaving traces of presence of its sea bed 
to vast altitudes on the highest mountains. But our Victorian 
geological authorities assert that these phenomena are the 
simple result of an (imaginary) system of upheaval, " easily 
understood ; " and that the changes traced by investigators 
as resulting from tidal waves during these periods of oceanic 
overflow, in subversion of masses of strata, torn down from 
lofty plateaux, or rifted out of the solid mountains by land- 
slips on a stupendous scale ; excavation of vast valleys and 
precipitous glens ; collection of water-worn fragments — often 
of huge, boulder-like dimensions — of the crystalline rocks, in 
ancient valleys, and their depositation in the eroded gutters of 
current flow ; the mechanical commingling of earthy matters, 
held temporarily in suspension in the agitated ocean until de- 
posited (as we see them presented in our railway cuttings), the 
coarser rubble first, in varied layers or strata, surmounted 
