And this movement is not embarrassed by any obstacle. The lower chains of hills do not arrest it, for it moulds itself to their form, sweeps through every opening between them, or overtops them. Valleys do not interfere with its onward march, for the frozen stream enters them, and levels them with the highest hills. It heeds not the precipice, for it leaps over it into the plain below,--a giant, frozen waterfall. Winter and summer are to it alike the same. It moves ever forward in its irresistible career,--a vast, frozen tide swelling to the ocean. It pours through every outlet of the coast ranges, down every ravine and valley, overriding every impediment, grinding and crushing over the rocks; and at length it comes upon the sea. But here it does not stop. Pushing back the water, it makes its own coast line; and, moving still onward, accommodating itself to every inequality of the bed of the sea, as it had before done to the surface of the land, filling up the wide bay or fiord, expanding where it expands, narrowing where it narrows, swallowing up the islands in its slow and steady course, it finally reaches many miles beyond the original shore-line. And now it has attained the climax of its progress. When, long ages ago, after pouring over the sloping land, it finally reached the coast and looked down the bay which it was ultimately to fill up, its face was many hundreds of feet high. Gradually it sank below the line of waters as it moved outward, and finally its front has almost wholly disappeared. [Sidenote: FORMATION OF ICEBERGS.] In a former chapter I have mentioned that a block of fresh-water ice floating in sea water rises above the surface to the extent of one eighth of its weight and bulk, while seven eighths of it are below the surface. The cause of this is too well known to need more than a passing explanation. Every school-boy is aware that water, in the act of freezing, expands, and that in the crystal condition fresh water occupies about one tenth more space than when in a fluid state; and hence, when ice floats in the fresh water from which it was formed, one tenth of it is exposed above, while the remaining nine tenths are beneath the surface. When this same fresh-water ice (which it will be remembered is the composition of the glacier) is thrown into the sea, the proportion of that above to that below being changed from _one_ and _nine_ to _one_ and _seven_, is due to the greater density of the sea-water, caused by the salt which it holds in solution. [Sidenote: FORMATION OF ICEBERGS.]