Pattison— Formation of Vallies, 161 



All the difficulties of a geological survey sometimes meet in the 

 space of a single flint. The gradated softness of edge in belts 

 widened by oblique section is however usually an instant means of 

 recognising them ; but in this stone the material is so fine that the 

 oblique edges are as sharp as the vertical ones. 



I could not without tediousness proceed farther in the description 

 of this stone ; it presents other phenomena peculiar to itself; but, 

 resuming the points hitherto stated, we may define the family of 

 agates, which it represents, as consisting of at least two formations 

 enclosed by quartz ; the inner formation being affected by disloca- 

 tions which do not pass into the outer one. Generally their colour 

 is brownish red and white, and their main material opaque and j asperine ; 

 their chalcedony developing itself subsequently and subordinately. 

 The crimson veins and stria3, which in some examples traverse the 

 inner formation, will furnish us with a study of separate interest 

 after we have obtained determinate types of other large and typical 

 groups : the minor details in each may then be examined with a 

 better field for comparison. For convenience sake I shall in future 

 refer to the group described in this paper as " Bipartite jaspers." 

 Their division may, indeed, be into more than two coats or forma- 

 tions, but the operation of a contractile force in one, which does not 

 affect another, sufficiently justifies the term for general purposes. 



III. — Formation of Vallies. A Description of Heudeshope. 



By S. E. Pattison, F.G.S. 



THE Heudeshope beck is a small feeder of the Tees, running 

 swiftly down a steep valley into the main stream, at Middleton 

 Teesdale. It is wholly in the lead-measures (Carboniferous lime- 

 stone), which are here nearly horizontal, undisturbed by trap, and 

 shew only a few faults, so small as not to affect the surface. The 

 great Teesdale fault operates on the other side of the main valley. 

 The Heude beck flows north and south. Its source is in the table- 

 land, forming the water-shed, between Weardale and Teesdale, 

 whence four or five streams issue in different courses. It is un- 

 obscured by the drift beds, which characterize the opposite lower 

 slopes of the Tees valley. It is excavated down to the solid rock, 

 the banks have been quite undisturbed by cultivation. It passes 

 through forty-three distinct alternations of grit, shale, and limestone, 

 to each of which the miners have given a distinct name ; it falls 

 about 1,000 feet in the six miles of its course. In the hope that 

 a tramp down by the side of its brawling rivulet, during the short 

 hours of a winter day, might illustrate some theory of valley - 

 formation, I devoted one of the last days of the year to the task. 



The summit of the table-land is formed by grit beds, called 

 Firestone, stratigraphically just below the Millstone grit. The 

 gorge begins by two scoop-like hollows, springing from the level. 

 These are covered with sharp blocks of unrolled, unscratched stone. 

 There is no nick in the table-land, no change of strata, no fault. 



