Rev. J. F. Blake— On the Motion of Qlaciert. 493 



places below the low-water level of the river, and when flooded by 

 an unusually high tide requires to be drained by steam power. This 

 may be due partly to shrinkage as mentioned above (although the 

 meadows are constantly in a state approaching saturation), or it may 

 be due to the deposition of mud in the bed of the river, consequent 

 on the supply of sewage from Colchester. 



At the part of Colchester called the Hythe {i.e. Wharf) the Colne 

 is navigable at high water, and granaries, etc., constructed on its 

 banks 200 years ago, are now frequently flooded in the basement by 

 high tides. Any slipping, such as I have suggested for Walton, is 

 here disproved by the existence of artesian wells extending deep 

 into the Chalk. An utterly imperceptible slip would certainly shear 

 off a three-inch bore-hole. 



In a creek near Steeple, east of Maldon, a certain row of piles, the 

 top of which used 60 years ago to be just uncovered at high water, 

 are now covered about i8 inches deep at most tides. 



On the south side of the Blackwater, the hills come down in a 

 point to high-water mark at the old Eoman and Saxon station of 

 Othonia or Ithanceastre, the ruins of which are exposed on the beach. 

 The tidal slope is about a mile and a quarter wide, and on the 

 outer edge of this — an almost impassable bed of mud — there are 

 other ruins, visible at dead low- water after storms have removed the 

 sand and mud, and consisting of foundations, wells, etc., the arrange- 

 ment of which is perfectly plain at such times. Alluvium is being 

 deposited between these ruins and the main land, so that if it is 

 a case of denudation since the erection of the buildings, the currents 

 must have altered considerably. 



North of the Crouch, the alluvium is 80 feet deep ; on Fowlness 

 and westward it is about 30 or 40, indicating the existence of the 

 Crouch Valley at a time when the land was at least 40 feet above 

 its present level. Fowlness, a wholly alluvial island, has certainly 

 been stationary since the Norman Conquest, so that any movement 

 which may be in progress does not include that area. 



III. — On the Motion of Glaciers. 

 By Eev. J. F. Blake, M.A., F.G.S. 



IN a recent Number of the Geological Magazine- Mr. Burns 

 assumes that Geologists in general seem to be satisfied with Mr. 

 Croll's theory of the motion of glaciers because they do not write in 

 refutation of it. I am convinced that with some at least it requires 

 no refutation, and its very obvious inadequacy is to them a sufdcient 

 reason for passing it over in silence. There cannot be wanting men 

 who, appreciating the difficulty of the problem, can only smile at 

 such a " solution." 



It seems absurd for one who has never seen a glacier in his life to 

 write about their motion ; and this has kept me silent on the point, 

 though I have given it some thought ; but if it is the case, as Mr. Burns 

 says, that many geologists are contented with an erroneous theory, as it 



1 See Geol. Mag. 1876, Decade II. Vol. III. p. 297. 



