38 baker's north YORKSHIRE. 



Whin-Sill, but it is quite evident that the Cleveland dyke is much 

 later in the date of its protrusion than the Teesdale mass, whilst 

 its mineral characteristics are not only distinct, but peculiar. 

 Indeed it is probably of Tertiary age, its direction indicating a 

 connection with the grand Irish-Scotch outburst of Miocene 

 times. It is a dark grey or bluish-grey rock, of augite andesite, 

 18 or 20 feet wide in Yorkshire, and even 80 feet near Great 

 Ayton, at its base. Generally its sides are not quite perpendic- 

 ular and the beds on the north of it are somewhat depressed. 

 In some places a tendency towards the prismatic type of structure 

 is observable in its masses. In the neighbourhood of the Tees 

 it is quite overlaid by glacial deposits. In the Ayton tract it 

 forms a conspicuous ridge and at Langbargh and in Kildale it is 

 extensively quarried for roadstone. From this last mentioned 

 dale its course lies along the dale of the Esk for some distance 

 in a line not far from the river. At Egton Bridge it forms a 

 steep scar in Limber hill, on the south side of the Esk, and from 

 thence turns south-east to the head of Iburndale, and at last, 

 after becoming considerably reduced in thickness it is lost 

 amongst the thick sandstones of the moorland mass not far from 

 the point where the main branch of the Derwent takes its rise. 

 (15) The Middle or Oxford Oolite Series. — The beds of this 

 series form the upper levels of the range of tabular hills which 

 is situated on the south of the moorlands of the Lower Oolite. 

 Except where it is broken through by the dales of the Derwent 

 district this range extends continuously from within five miles of 

 Thirsk eastward to the sea-coast, measuring thirty-five miles from 

 east to west. The elevation of its table land above the sea-level 

 lessens as we proceed from west to east with remarkable regularity. 

 Hambleton End is 1289 feet high, Easterside 1048 feet, Helm- 

 sley Moors 1078 feet, Levisham Moor 882 feet, Hackness Moor 

 714 feet, Oliver's Mount 490 feet, and Gristhorp Clifif 295 feet. 

 Along the whole of this line the beds of this series are escarped 

 towards the north over the Lower Oolite with considerable 

 abruptness. From Hambleton End the range extends due south 



