Coming south from these high latitudes, I left blocks of Finnish granite in plains near Berlin. In my view Irish glaciation is but a small part of something far greater, which acted continuously from the White Sea down to the Kerry sea-loughs ; and the question now is, what was the nature of the engine that did all this vast glacial work?
XVII. Land-ice or sea-ice. — Nine years ago my smaller collection of facts led me to account for all glaciation by causes upon the extreme scale of the existing arctic current and Greenland ice, which I travelled to look at afloat off Labrador and Newfoundland. As my collection of facts grows, I am led towards something still larger. Even an extension of the climate of Greenland to Ireland, and the shifting of the arctic current to the Baltic, would hardly account for marks which I have seen and which I have tried to describe here and elsewhere. When I review all that I have seen in Finland and Scandinavia, in Iceland and Labrador, in Greece, in the Alps, in Spain, and in America west to the Mississippi, and try to combine what I have seen with all that I have learned from writings, maps, and pictures, the whole of my knowledge of facts leads me to a very great extension of all glacial systems, and to a union of many to form one great Polar system, which moved southwards, and reached far beyond the latitudes of New York and Rome. Near New York, for example, the ice came from Canada, and it was over 2000 feet thick when it passed along the scarped face of the Catskills in the direction of the flow of the Hudson river.
I thought that icebergs floating in an arctic current would account for horizontal grooves, which I copied by rubbings all the way up the face of the mountain. The uncertainty of the marks upon the top, where water would flow into the next valley, confirmed that opinion. I now begin to think that the ice which passed over the site of New York seawards in the latitude of Madrid may have been part of a crust which spread from the Pole down to that latitude at least, and there was over 2000 feet thick. My theory has grown with my knowledge of facts. My separate icebergs have joined together. To all that I have said in ' Frost and Fire ' I have added more solid ice, and, as I believe, on solid grounds.
XVIII. Theory. — This is the purport of the story which I have deciphered from glacial rock-inscriptions in Ireland and elsewhere : — During a late geological period; land in the northern hemisphere was covered by thick crusts of ice, like ice in the southern hemisphere. The crust was continuous then down to low latitudes, as it is now in high southern latitudes. Where it ceased to be continuous, mountains supported large and small local systems, as mountains now do. But the separate systems approached and may have reached to the equator, as said by Agassiz. There was then, as there is now, a general movement from north to south in high latitudes. Where the water was shallow, glacier-ice grounded ; where it was deep it floated ; and the depths at which ice grounded were proportionate to the depth of the ice. At 2000 feet berg-ice, which
