edge, but that much more remains still to be determined. It seems as likely that in this problem geology and meteorology will pass the word of command to physics as the converse. At present our knowledge of a definite limit to geological time has so little precision that we should do wrong to reject summarily any theories which appear to demand longer periods of time than those which now seem allowable. In each branch of science hypothesis forms the nucleus for the aggregation of observation, and as long as facts are assimilated and co-ordinated we ought to follow our theory. Thus, even if there be some inconsistencies with a neighboring science, we may be justified in still holding to a theory, in the hope that further knowledge may enable us to remove the difficulties. There is no criterion as to what degree of inconsistency should compel us to give up a theory, and it should be borne in mind that many views have been utterly condemned when later knowledge has only shown us that in them we were only seeing the truth from another side.
An Inventory of the Glacial Drift.—Vice-President Chamberlin, in his address before the American Association's section of Geology and Geography, presented "An Inventory of our Glacial Drift." Having described the boundaries of the drift as represented on a wall-map, the speaker remarked that a wealth of significance lay in the sinuosities, vertical undulations, and varying characters of the southern border. It undulates over the face of the land essentially much as an arbitrary line from New York Harbor to Puget Sound, and could be reduced to horizontality—as it must have been to have marked the margin of some ancient ice-bearing body of water—only by incredible warpings and dislocations. The border presents three notable phases: one part terminating in a thickened belt, a terminal moraine; another in a thin margin; and a third in an attenuated border of scattered pebbles. The morainic border prevails in the Atlantic region and on or near the limit as far west as Central Ohio. Throughout the rest of the stretch to the Rocky Mountains the attenuated edges prevail. Of unstratified bowldery clays or tills, there is the richest variety, ranging through diverse combinations of material, texture, and aggregation. Of moraines, terminal, lateral, medial, and intermediate varieties are found. The great terminal moraines overshadow all others in interest and importance. Outside of the chief moraines are occasional belts of older drift aggregated in the similitude of peripheral moraines. Back from the two principal terminal moraines lie similar partially determined belts, usually of less prominence and continuity. Our most unique moraines are the interlobate, developed between the tongues into which the ice-sheet of the second epoch was divided at its margin, of which about a dozen, in half as many States, are recognized. Beautiful lateral moraines abound in the mountainous regions of the West, and some were developed by local glaciation supervening upon the ice retreat of the East. Our medial moraines are unimportant, and confined essentially to mountainous glaciation. Allied to the true moraines are special forms of aggregation of the sub-glacial débris. Two classes commonly embraced in the assorted drifts should be excluded from them: the "orange sands" of the Mississippi Valley, which do not appear to possess the distinctive characteristics of glacial gravels, but are residuary in aspect; and the secondary drifts, or those that have been reworked by wholly non-glacial agencies. Eliminating these, two classes of products of glacial waters working co-ordinately with the ice are recognized: those that gathered immediately within and beneath the ice-body itself, or against its margin; and those which were borne to distances beyond its limit by the glacial drainage or by peripheral waters. The products embrace a great variety of sub-types of gravel-heapings, including isolated mounds, conical peaks, clustered hummocks with inclosed pits and basins, and sharp, steep-sided ridges, often of phenomenal length, all possessing great irregularities of material and stratification, embracing frequently, manifest disturbances. The elongated variety, resembling the great osars of Sweden, are finely developed in Eastern New England; while the hummocky variety, constituting the ill-defined class of kames, are abundant throughout New England, New York, Northern New Jersey, Pennsylvania,
