material, except, of course, as it took place by virtue of the falling of the latter through crevasses to the base, and by mechanical intermixture of the two at the edge of the ice. The amount of englacial till under this view is little more than that which was lodged in the body of the ice in its passage over the knobs and ridges of the hilly and semi-mountainous regions of the north. To this is perhaps to be added occasional derivatives from the more abrupt prominences of the paleozoic region and the superficial dust blown upon the ice from the surrounding land, which was probably the chief source of the silty material intermingled with the superficial boulders. The total amount is thus quite small, though important in its significance. The eskers and kames of the region are made up of derivatives from the basal material as shown by (1) the local origin of the material in large part, (2) the mechanical origin of the sands and silts, (3) the not infrequent glacial markings of the pebbles and boulders, and (4) the disturbed stratification of the beds.[12] If I am correct in respect to the kind and amount of the englacial and superglacial material, it is obvious that eskers and kames, such as are found in the interior, could not be derived from englacial or superglacial sources. The term englacial as here used does not include such materials as may be lodged in the basal stratum of the ice and brought down to the actual bottom by basal melting. [12] See "Hillocks of Angular Gravel and Disturbed Stratification," Am. Jour. Sci. Vol. XXVII., May 1884, pp. 378-390. The conclusions drawn from the phenomena of the plains of the interior are not necessarily applicable to more hilly or mountainous regions. =T. C. Chamberlin.= =_Studies for Students._= DISTINCT GLACIAL EPOCHS, AND THE CRITERIA FOR THEIR RECOGNITION.[13] [13] Read before the American Geological Society at Ottawa, Dec., 1892. I. =Introduction.= It has long been evident that writers on glacial geology are not at one concerning some of the important questions which underlie the interpretation of the history of the glacial period. Certain recent publications have served to emphasize the differences between them. There are two questions, at least, concerning which there must be agreement, or at any rate a common understanding, before existing differences can be eliminated or justly evaluated. When the answers to these questions have been agreed upon, or when the positions of the contending parties are clearly understood, it may be found that some of the apparent antagonisms have no better basis than differences in definition. Stated interrogatively, the two questions referred to are these: 1. What constitutes a glacial epoch as distinct from other glacial epochs? and 2. What are the criteria for the recognition of distinct glacial epochs, if such there were? II. =The Idea of a Glacial Epoch.=