So our cross sections, cut with a knife in the delta, and the winding cake extending upstream in the cavern showed topset, foreset, and backset strata after draining the tank and lifting out the apparatus. From the embryo delta the flood-plain beds overlap the earlier frontal, or foreset, beds. The frontal beds are always under the lagoon. The flood-plain beds (topset) were made by a meandering river course under the air. Always this plain is built at beach level as a wash fan shaped like a leaf, with the cavern stream bottom as the stem of the leaf. New England has been covered with mountainous ice, miles high. Subglacial streams and subglacial clear ice caverns are abundantly found at the lower ends of all glaciers in the world. They merely represent the melting snow and ice in pulses of sunshine, snow at the source, ice in the course, crevasses and gravitation making water seep through. This water shapes a channel for itself and erodes a sewer system of scouring along the bottom of the subglacial valley. This grinds and melts the bottom ice into arched caverns; and the sediment builds up on the stream bottoms, eventually carving the roofs of the caverns into high arches or arcades. The subglacial caverns are self constructed drainage pipes. The glacial stream is really a river flood cutting its valley. The ice river grinds and scrapes, and the water under the ice pipes and drains the melting. The ice carries chisels of broken rock. The enormous weight, in gliding plane layers of ice, flows in accordance with the crystal laws of snowflakes and ice crystals. The moraines, or debris fields, at the sides and on top and underneath the eroding ice jumble yield mud and sand and boulders. The torrent underneath removes the rubbish. The delta in front follows laws of sedimentation. If there is no lake in front, the delta is a flat wash fan, or valley flood plain. All these things become clear to the student who makes a baby glacier out of tinware, sand, a tank, a hose, and a faucet. I have spoken of cataclysms, or what early geologists called catastrophe, happening occasionally in the world of erosion and subterranean geysers. Such were the Yakutat crash and the Bandaisan explosion. But each glacier-period field, like an ice mountain over Europe and America, constituted a cataclysm lasting 500,000 years, and this happened four times even in the centuries of early man. The Mediterranean and the Great Lakes are offspring of such cataclysms. But Lyell carried the doctrine of uniformity to extremes; he thought that what man sees is what always happens. I do not believe Lyell ever realized that earth or sun might conceivably explode in a month of our time. Again, this is not likely.