The district in which my observations have been made may be roughly described as that part of the Vale of Mowbray which lies between Ripon, Thirsk, and Boroughbridge, being bounded on the west by the river Ure, and on the east by the foot of the Hambleton Hills. Through the centre of this district runs the river Swale. This piece of country seems to be very rich both in quantity and variety of erratic rock fragments. I have not confined my observations to boulders of large size, but extended them to any fragments, however small, which seem interesting as part, of the drift. I shall first give a list, though necessarily an imperfect one, from a petrological point of view. I shall then endeavour to refer the boulders to their original stratigraphical position, mentioning the characters of the rocks or of their contained fossils which have guided me in this. Next I shall make some remarks on the local distributions of these erratics, and the direction of the ice or water-currents by which they were brought into the place they occupy. I shall begin with the Siliceous Rocks as they form a large majority. Fragments of sandstone are present of every size, from great boulders to fine sand, of every degree of hardness, from an almost flinty rock to stone so soft that it perishes after a very short exposure to the weather. In texture they vary from the roughest grits to the finest possible sandstone. In colour there is ...