April 1, 1897.] 



KNOWLEDGE. 



93 



Carboniferous rocks overlie the Upper Silurians uncon- 

 formably, and at a much lower angle. 



The Pennine mountains of England, with which may 

 be associated the Cheviots on the Scottish border, extend 

 from the northern boundary of England to Derbyshire 

 (summit elevation. Cross Fell, two thousand eight hundred 

 and ninety-two feet), and are formed of Carboniferous or 

 Mountain Limestone, Yoredale rocks, and Millstone Grit ; 

 but of Igneous rocks there is an immense mass in the 

 Cheviots, and in Derbyshire the " Toadstone " makes its 

 appearance amidst the Carboniferous Limestone. The whole 

 range forms a great anticlinal with the Millstone Grit, 

 dipping both on the east and on the west under the Coal 

 Measures of the lower levels on either side. The age of the 

 Pennine range must therefore be later than the Car- 

 boniferous period, but earlier than the Triassic, the rocks 

 of which epoch extend on each side approximately hori- 

 zontally. 



The western elevations of England are very ancient 

 lands. The most southern of these, the Malverns (Worces- 

 tershire Beacon, one thousand four hundred and forty-four 

 feet), which form a very perfect mountain range on a small 

 scale, have a central ridge with expanding base of Syenite, 

 a varying rock largely made up of felspar and hornblende. 

 Elevation took place here in very early times, as the HoUy- 

 bush Sandstone of Cambrian age lies quite unconformably 

 on the upturned edges of the crystalline Silurian rocks. 

 Silurian rocks are also high on the flanks of the Malverns, 

 with a high dip ; and so it is evident that although there 

 may have been a pre- Cambrian ridge, a subsequent depres- 

 sion took place which extended through the Devonian 

 period. But on the eastern side of the Malvern range 

 Triassic rocks abut at a low angle against the Syenite, 

 and extend to the east almost horizontally ; while a "fault " 

 with a remarkably great ' ' throw " extends north and south 

 for many miles, dividing the low lands of the Severn Valley 

 from the uplands of the west. 



A little to the north, in Shropshire, the remarkable 



Herefordshire 



4 



Caer Caradoc, Corndon, the Clee HiDs, and the Wrekin, 

 that stand out very conspicuously, and are due to being 

 altogether or in part formed of hard Igneous rock that has 

 resisted denudation. In the case of the Clee Hills, a 

 sheet of basaltic rock forms the summit, and through 

 this shafts are sunk to work the coal of the underlying 

 Coal Measures. 



The Mendips are a very interesting group of elevations 

 that illustrate rock-folding on a grand scale, and subsequent 

 to Carboniferous times. The mass consists of Old Red 

 Sandstone and Carboniferous Limestone, both greatly folded 

 and so presenting strata at a high angle of inclination. 

 That the elevation giving this dip was pre-Triassic is shown 

 by the fact that rocks of Triassic age lie so unconformably 

 that they are approximately horizontal on the highly 

 inclined Carboniferous rocks. 



The Ocrynean hills of Devonshire and Cornwall (Yes 

 Tor, two thousand and fifty feet) are largely formed of the 

 granites that are so conspicuously seen in the tors of 

 Dartmoor and some Cornish localities. That these granitic 

 masses took their present relative position to the neigh- 

 bouring sedimentary rocks after the formation of those 

 rocks is shown by the adjacent uptilting and metamor- 

 phosation. A study of rocks enwrapping the granitic 

 masses places the age of the uprise as post-Devonian. 



Leaving the motmtains and hiUs of the North, the West, 

 and the South- West of England, and coming to the central 

 area, it wiU be fomid that the elevations there consist 

 chiefly of much newer formed land than the elevated areas 

 hitherto considered. But there is a notable exception. 

 The hilly district constituting Charnwood Forest, in 

 Leicestershire, is formed of rocks that are so ancient 

 that it has been a most difficult problem to determine 

 their age. They were once thought to be Igneous, 

 so extreme has been their metamorphosation ; but 

 they are now determined to be altered sedimentary rocks, 

 by some thought to be pre-Cambrian, and by others 

 Cambrian. An elevation, however, certainly took place 



Beawii' 



WORCESTERSHIRE 



Section across the Malverns. 1. Malvern Rock (Syenite, etc.). 2. Caradoc. 3. Wenlock. 

 4. Old Ked Sandstone. 5. Bunter. 6. Keuper. 



Longmynd Hills (summit, one thousand six hundred and 

 seventy-four feet), consisting of the oldest Cambrian rocks 

 in a nearly vertical position, with Upper Silurian beds lying 

 on their truncated edges, form classic ground for geologists. 

 The verticality of the strata, estimated at twenty-five 

 thousand feet in thickness, and its truncation, denotes great 

 elevation, with folding and subsequent denudation on an 

 enormous scale, and, later, a depression to allow of the 

 deposition of Upper Silurian rocks. But as these latest 

 formed rocks are at a high level it will be necessary to fix 

 the age of the Longmynds as post- Silurian. The western 

 district of England is diversified by some bold hiUs, as 



LONGMYNDS 



before the Carboniferous period, and another before the 

 deposition of the Triassic rocks that lie all around the 

 area, almost horizontally. At a little distance to the 

 east is the remarkable mass of rose-coloured horn- 

 blendic granite forming Mount SorreU, also in its elevation 

 pre-Triassic. The central hills of England are, however, 

 chiefly of Secondary geological age, and therefore form 

 much newer land than that of any of the areas hitherto 

 considered. 



The Chalk hills forming the south-eastern elevations of 

 England have certainly been elevated since the Eocene 

 period, for they carry on their surface many Eocene 



Section across the Longmynds, Shropshire. 1. Cambrian. 2. Caradoc or Bala. 3. Upper Llandovery. 



4. Wenlock Series. F. Faults. 



