of Edinburgh, Session 1884-85. 
87 
not produced deposit in all rivers, for the fact seems just as certain, 
on physical grounds, that they will not produce accretion in some 
rivers as that they will produce it in others. It is essential that 
before accretion can, in any case, take place there must be matter in 
suspension, or, in other words, there must in some part of the river 
be water in such rapid motion as to break up and move the materials 
of the bottom and sides of the channel, while at some other part of 
the river there must be such retardation of the velocity of the 
water as to cause the deposit of the matter in suspension; and, 
besides this, there must be a large receptacle to contain this matter, 
and sufficiently sheltered from waves and currents to retain it after 
deposit. 
The Clyde . — Having for the last twelve years acted as engineer 
to the Clyde Lighthouses Trustees, who are the Conservators of the 
lower estuary of that river, and having during that time been 
engaged in conducting very extensive dredging operations, I am . 
necessarily fully acquainted with its peculiarities, and can state that 
there is only one point of resemblance of any consequence between 
that river and the Mersey, viz. , that the lower land-locked estuary of 
the Clyde is about the same in width as that of the widest part of 
the Mersey below Halehead. But then there is no training wall Con- 
nected with the shore for guiding the channel through this wide 
estuary, so that we can get no information on the subject at 
issue. The walls which do exist in the Clyde are mainly in the 
upper part of the river, where the navigable channel is only about 
400 feet wide, and where there is no large space left for silting up 
to take place between these walls and the land. 
With the one exception of the wide estuary to which I have 
referred, none of the characteristics which are favourable to deposit 
exist in the Clyde, as I will now show. The rise of tide in the 
Clyde is only 10J feet, as against 30 feet at the Mersey. The 
maximum velocity of the tidal flood current is only about half a 
mile per hour, as against 7 at the Mersey. There is no tidal bore at 
the Clyde, and a very rapid one at the Mersey. There is neither a 
bar nor any heavy breaking waves at the Clyde, but there are both 
at the Mersey. There is only 1 cubic inch of silt to 1 cubic yard 
of water at the Clyde, and 33 cubic inches to 1 cubic yard at the 
Mersey. 
