102 ME. L. J. WILLS Olf LATE GLACIAL AND [June I912, 



approximatiEg froml20 to 150 feet above the present river. These 

 are early flood-gravels, and are connected with the first stages in 

 the formation of the valley. They indicate that the earliest post- 

 Glacial drainage took the course now occupied by the Ceiriog Valley, 

 and that this stream vras never captured by the Dee after the 

 manner of the ]\Iorlas Brook diversion. Their early date and 

 their intimate connexion with the Glacial deposits are shown by 

 the continuity of some of them with moundy Glacial gravels near 

 Chirk Bank. 



Later stages in the erosion of the valley are recorded by several 

 large river-terraces at much lower levels than the above-mentioned 

 gravel-flats. Their heights above the Ceiriog show them to be 

 capable of a rough comparison with the 60- and 40-foot terraces of 

 the Dee. 



Thus the post-Glacial origin of the lower part of the Ceiriog 

 valley is as clearly demonstrated as that of the Dee between Cefn 

 and Overton. 



(7) The Pre-Glacial A^ alley near Holt and Chester. 

 (See fig. 3,' p. 193.) 



The occurrence of a pre-Glacial valley in the Chester district 

 was dealt with by Dr. Strahan ^ in 1890 and 1898. He records a 

 number of borings under the estuary of the Dee in which the base 

 of the Drift lies far below sea-level, the greatest reliable depth 

 being 195 feet near Sandycroft. This means that the surface of 

 the solid rock is here 184 feet below Ordnance Datum, whereas 

 the present river is, of course, at sea-level. 



The course of this buried valley was roughly indicated by the 

 following depths below sea-level at which either solid rock was 

 reached or at which wells or borings ended in the Drift (see 

 %. 3):- 



Feet. 



i^ear Queensferrj —146 and possibly —177 



„ Sandycrolt -181 and -132 



„ Saltnev -134 



„ Dodlestou - 90 



„ Pulford - 20- 



„ Eaton Hall - 40" 



It has now been traced some 7 miles farther south by means of 

 the following observations of depths : — 



Feet. 



Near Horslev Hall - 25- 



„ Eidley Wood -30^ 



At D Litton Diffeth - 10"^ 



AtRodensHali -30 



1 A. Strahan, ' The Geology of the Neighbourhoods of Flint, Mold, &Euthin ' 

 Mem. G-eol. Siirv. 1890, and'Sapplement, 1898. Dr. Strahan informs me that, 

 in view of more recent borings at Sandycroft, the record of 300 feet of Drift 

 must be disregarded. 



2 This indicates that the solid rock was not reached, and that the depth 

 below sea-level may be greater. 



