ON PHYSICAL AND ENGINEERING FEATURES OF THE MERSEY. 553 
tained its general conditions, both as regards position and capacity, with 
‘singular regularity, so that the conditions of navigation have remained 
practically uniform. 
This indicates the value of the tidal volume flowing into and out of 
the Upper Estuary, and clearly points out the vital necessity of main- 
taining it undiminished and untrammelled to the fullest possible extent. 
The Bar, as is doubtless well understood, is a sandy accumulation or 
ridge, with a long sloping foreshore on each side, stretching across the 
mouth of the main channel ; on plan its form is that of an irregular 
‘curve, somewhat in the shape of a horseshoe with its convex side seaward, 
separating the deep water of the channel from that of the offing. It is 
the result of the loss of concentration of the current due to the channel 
departing from its regularity of form where it issues from the banks 
and meets their outer or sea slopes. It is joined up on its north flank to 
the tail or westernmost extremity of the most seawardly bank of the 
group known as the Zebra Flats, which forms an extension of Taylor’s 
Bank under water, and on the south to the western spit of the 
‘Little Burbo. 
The Bar is not constant in position, but has been found to be moving 
slowly seaward, in accord with the growth of the banks in a like direction, 
‘maintaining, however, its general characteristics. [F urther on, the 
author refers to the works undertaken to give increased depth of 
water on the Bar. | 
In addition to this main channel, there are two minor or subsidiary 
‘channels, viz.—the Formby Channel and the Rock Channel. The 
former is a prolongation nearly in the same direction as that of the inner 
reach of the main channel, which it leaves at a point abreast of the 
Crosby Lightship and continues in a northerly direction to the Formby 
‘Spit, after which it reaches the open sea, five miles from its junction with 
the Crosby Channel. It is narrow, shallow, and somewhat tortuous when 
it leaves the main channel, but is thoroughly buoyed, and is used by 
small vessels proceeding to and from the north, as it saves a détour of 
several miles. 
The Rock Channel, so called from the rocks which crop up at the 
point at New Brighton, where it leaves the main channel, runs from that. 
point westerly, nearly parallel to the Cheshire shore for a distance of six 
miles, when it turns to the north-west and passes into the Bay by an 
outlet known as the Horse Channel, between a spit of the Great Burbo 
and the East Hoyle Bank, which separates the water of the river 
Mersey from that of the river Dee. 
Before the Crosby Channel with its bar entrance became stable and 
pronounced, the Rock was the chief channel to and from the port, owing 
to its position relative to the prevailing winds. Its main body was then 
wider and deeper than at present, it having considerably deteriorated 
‘of late years and come inshore, while the Horse entrance has become 
narrower and more difficult. 
The whole of the entrances to the port are buoyed and lighted on the 
most approved system. Powerful distinguishing lights to serve both the 
Crosby and Rock Channels are placed on the land at the river mouth, at. 
New Brighton and North Wall. In the main channel floating lightships 
are moored as follows :—the Crosby light at the point where the Crosby 
Channel changes its direction ; the Formby light about halfway between 
the Crosby and Bar lights, the latter of which is moored about 13 mile 
