GEOLOGY 9 



of the British Association ; at that time (1906) several large brick pits at 

 Dringhouses afforded sections of a thick deposit of laminated clays, but 

 these are now either filled in or flooded. 



Were the superficial deposits to be removed the position of York would 

 be seen to lie in the centre of a plain occupied by Triassic rocks. This 

 plain, the Vale of York, is bounded on the west by the uprise of older 

 rocks less easily eroded than the sandstones and marls composing the 

 Trias, on the east by newer rocks overlying it. To the north-north-west 

 the plain narrows towards the Tees valley, and is known as the Vale of 

 Mowbray, southwards it widens to the Humber and is continued in the 

 Vale of Trent. The western margin is everywhere formed by Permian 

 rocks, of which the dominant member is the Magnesian Limestone, but at 

 the base of these is a great unconformity. In the south they are underlain 

 by the Coal Measures, forming the great Yorkshire coalfield. During the 

 meeting of the Association a visit will be paid to the Conisborough area, 

 where beds near the top of the Middle Coal Measure will be seen imme- 

 diately beneath the Permian, but not far from Tadcaster the whole of the 

 Coal Measures is cut out and the Permian rests on Millstone Grits. A 

 geological excursion to Tadcaster and Bramham will demonstrate this point. 

 The northern boundary of the ' concealed coalfield ' beneath the Permian 

 and Trias is not known, but the balance of evidence is in favour of a west 

 to east line. It may safely be assumed that no Coal Measures are present 

 beneath York. 



The eastern margin of the Triassic plain is formed, from north to south, 

 by the high ground of the Hambleton Hills, the Howardian Hills, and 

 the Wolds. The two former consist of Jurassic rocks, the last of chalk. 

 It is impossible in this short account to give a detailed description of the 

 beds or to discuss the many interesting problems which their characters 

 and distribution suggest, but sufficient may be said to indicate the main 

 points which will arise on the various excursions. In the Hambleton 

 Hills the escarpment shows a complete succession from Lower Lias to the 

 Calcareous Grit. In the Howardian Hills the highest ground is occupied 

 by beds belonging to the Lower Oolites. These two blocks are separated 

 by a trough due to faulting, known as the Gilling Gap, in which most of 

 the ground is occupied by Kimeridge Clay. The gap forms a connection 

 between the low-lying ground of the Vales of Mowbray or York on the 

 west and the Vale of Pickering on the east. 



Due east from York and at a distance of about 12 miles is the escarpment 

 of the Chalk Wolds. It is recorded that when William Smith first visited 

 York he climbed to the top of the Minster tower and saw the W^olds in the 

 distance. From the form of the ground he recognised that the rock was 

 chalk, thus confirming his ideas of stratigraphy. Prof. Kendall has 

 suggested that that day was the birthday of stratigraphical geology. A 

 word of warning may be inserted here. From the same or any other 

 elevated viewpoint, the visitor to York will see in the distance a white 

 horse cut on the scarp of the hills ; if he comes from the South of England 

 he may assume that he is looking at the chalk, but he would be wrong. 

 This white horse is cut in Corallian rock on the flank of the Hambleton 

 Hills, almost due north from York. 



