THE RIVER MERSEY. 27 



of ordinary spring tides — the river rapidly widens into a very extensive reach 

 or reservoir, soinetimes called the upper estuary ; from which the tide, after 

 sending an offshoot into the Weaver, passes into the upper reaches of the 

 river through the smaller gorge of Runcorn-gap. After traversing a series 

 of reaches and gorges of less and less importance, and surmounting a low 

 weir at Howley-Ioeks (Warrington), its further progress is finally barred by 

 the Woolston-weir of the Mersey and Irwell navigation. This weir is about 

 four miles above Warrington ; twenty-two miles above the Rock Point, New 

 Brighton ; and thirty-four miles above the bar of the Victoria Channel. 



In the first instance, the phsenomena of the upper estuary, and those of the 

 \nter estuary or Liverpool Bay, may be most conveniently considered apart; 

 the results of their investigation can afterwards be combined. 



Liverpool Bay. — The earliest authentic survey of Liverpool Bay, published 

 within the period assigned to this inquiry, is that of Captain George Thomas, 

 R.N., which was taken in 181S, and published in May 1815. The next 

 authentic survey is that of Captain H. M. Denham, R.N., in 1833. Both 

 these surveys were made by order of the Admiralty, in consequence of the 

 great anxiety and alarm experienced by the local authorities, arising from 

 the important changes which took place in the channels prior to each of the 

 above dates. 



The changes of the later period continuing, — they were in fact the precur- 

 sors of the substitution of new outlets for the old ones, — the surveys were 

 repeated by Captain Denham, in 1835 and 1837. 



North Channel. — On comparing the charts of 1813 and 1833, it appears 

 that at the former date the Northern Channel, which Avas previously divided 

 into two portions, called the Crosby and the Formby Channels, maintained 

 an even course until it had passed Crosby Point, where it separated into two 

 outlets; one over a bar, with from one to eight feet of water, into the old 

 Formby Channel, in which were from one and three-quarters to six fathoms; 

 and thence over another bar seaward with from one to eight feet of water. 

 The other outlet, called the South Channel, was to the southward and west- 

 ward, and passed between the Jordan and Great Burbo Banks, having from 

 two to six fathoms, diminishing on a seaward bar to 7 feet. In this survey 

 Formby Bank is insulated and covered at four hours' tiood. 



Formby Bank. — In 1833, twenty years later, Formby Bank had attached 

 itself to the main shore ; and the old Formby Channel was almost land-locked, 

 and had no communication with the Crosby Channel, except over a 6-foot 

 bar, between Jordan and Formby Banks. The depth of water on the seaward 

 bar of this channel had increased in places to 13 feet. 



New Channel. — The South Channel of Thomas's survey appears to have 

 shifted upwards of a mile to the southward, and acquired nearly a true east 

 and west bearing ; and had a bar with 10 or 11 feet of water. It was called 

 by Denham the New C'iannel. 



Zebra Channel- — Between the Formby Channel and the New Channel 

 another outlet was opened, having a minimum depth of 2 I'eet, and called the 

 Half-tide Swatchway, or Zebra Channel. 



Mad Wliarf. — Mad Wharf, a large bank adjoining Formby Point to the 

 northward, had elongated upwards of 2200 yards in that direction, and its 

 area considerably enlarged. 



Many changes took place in the position and magnitude of the minor 

 banks adjoining the seaward entrance of the Northern Channel ; some of 

 which, as the "middle patch," nearly disappeared ; whilst others enlarged 

 their area, or sprang altogether into existence. 



Victoria Channel, — Between the survey of 1833 and those of 1835 and 



