14 March, The Superficial Geology of Manchester. 



99 feet of sands^ and clays, while at Hugh o' th' Wood Colliery in 

 Prestwich Clough the shaft section shows a thickness of 156 feet. 



Viewed broadly, therefore, the Drift around Manchester is 

 thickest on the north and east, and thins to the south and west. 



Present Topography and its Relation to the Drift 



The physical map of Manchester, PI. I., contoured to every ten feet 

 shows remarkable diversity in the character of the surface in differ- 

 ent areas. In the north-west the surface is very irregularly broken. 

 In the south and east the contours run very smoothly north-west 

 to south-east. Up to the 200-foot line the surface slopes gently to 

 the River Irwell. From the 200- to the 250-foot contours the gradient 

 increases. Between the 250- and 350-foot lines occurs another belt 

 of more level land. The most striking feature of the map is the 

 deeply trenched character of the valleys, which in the north-west 

 about Kersall and Prestwich entirely change the nature of the surface. 

 Instead of the regular contours of the south and east, the ground 

 shows a relatively high sand plateau, deeply dissected on the margins 

 by a series of ravines. ' On the right bank of the Irwell the ground 

 rises from the river steeply, and relatively unbroken. 



Outside this area of irregular surface the levels stretching from 

 south-west to north-east are only cut by the valleys of the Irk 

 and Medlock. In the north-east, by Oldham, the latter river has 

 trenched deeply into the solid rock. 



Comparison of the physical map with one showing Drift thick- 

 ness makes it clear that the area of broken country does not coincide 

 with that of maximum Drift thickness ; but if the comparison be 

 made with a map showing the distribution of the sands and clays it 

 becomes evident that the irregular surface occupies the same position 

 as the Glacial sands, which stretch from Boggart Hole Clough across 

 Prestwich to Pendleton. 



It is quite natural that the rivers should cut deep gorges here, 

 as the loose nature of the sands makes erosion easy ; while on the east, 

 where the almost equally thick deposits of Moston, Newton Heath 

 the Ashton occur, the heaviness of the clay would prevent such rapid 

 wearing. 



The Pre-Glacial Surface 



Unfortunately the records of the depth of the solid rock below 

 the surface are too few and scattered to make it possible to draw 

 a map of the pre-Glacial surface, except in the area of central Man- 

 chester and as far to the south as Alexandra Park. 



This map, reproduced in PI. II., shows that there is no corre- 

 spondence between the present and pre-Glacial river valleys. One 

 pre-Glacial valley is clearly seen near the centre of the map, where 

 the pre-Glacial contours, which are marked in thick lines, trend from 

 S.S.W. to N.N.E. This valley can be traced upwards from Brook's 



