The investigation of submarine canyons has been actively pursued in the United States of latter years, principally due to the activities of F. P. Shepard. The Coast and Geodetic Survey has mapped a large number of these interesting chasms, both along the Atlantic and Pacific continental slopes, by sonic soundings; Shepard himself added data by soundings and dredgings along the Californian coast; Stetson performed current measurements, dredgings, and sampling in the canyons off the east coast. The number of data is steadily increasing in the United States, and it is to be hoped other nations will also become active, for much still remains to be learned before a comprehensive view of the many-sided problem can be obtained.

The Bergschrund Hypothesis, when it was enunciated by Willard Johnson (I) at the end of last century, was almost universally welcomed as an explanation of cirque formation. Since that time it has continued to dominate the literature on glacial sculpture. Gilbert (2) and Hobbs (3) in America, Wright (4) in this country, and Penck (5) and de Martonne (6) on the Continent follow his ideas with only very minor modifications. The essentials of this hypothesis were, however, outlined by W. M. Davis (7) contemporaneously with the publication of Johnson's 1899 paper.

In this country the species which at one time or another have been assigned to the genus Platycrinus amount to a considerable number. From the works of J. S. Miller, J. Phillips, A. Goldfuss, T. and T. Austin, F. McCoy, de Koninck and Le Hon, etc., one might make up a list of well over a score of species, but to identify specimens from the British Carboniferous limestones with the figured or described species is a very difficult matter. This is due chiefly to the poorness of the illustrations of the species concerned or, when the figures are passably good, to the lack of prominence given to the more important characters of the calyx. Two at least of McCoy's species and one of Phillips's are not illustrated at all. There is also some confusion regarding certain species which seem to have been figured more than once under different names. In the process therefore of identifying specimens it soon becomes evident that few of the species have been placed on a satisfactory basis and that as a group the British Platycrinidae is much in need of revision.