Mr. George Tate on the Cheviots. 863 



near to Harthope ; peroxide of iron is in small veins on the 

 north side of Cheviot ; and iron pyrites are in Homildon 

 Dene; but, excepting the iron diffused through the horn- 

 blende and augite, the quantity of iron in the Cheviots is 

 small. 



Eelation to Stratified Eocks. 



Porphyries and syenites, as well as other igneous rocks, 

 have been erupted at different periods ; but as mineral char- 

 acter alone is no ceitain test of age, and as, moreover, such 

 rocks contain no organic remains, we must seek a chronology 

 from other sources, more especially from their relative posi- 

 tion to other rocks whose age is ascertainable. We must, 

 therefore, examine the stratified rocks which flank the Chev- 

 iots, before we can form an idea of the origin and age of these 

 erupted mountains. 



1. Beginning with the oldest stratified rocl^s, we find 

 Greywacke or Camhro- Silurian beds highly tilted up against 

 the porphyry in the valley of the Coquet above Philip and 

 extending beyond the source of that river into Scotland. 

 Eastward of Makendon they are well exposed in a high cliff; 

 the Roman camp — Chew Green — rests upon them, and some 

 of its rampiers are natural walls of greywacke in situ, with 

 the rock removed on both sides. They consist of distinctly 

 stratified greywacke slate, which is much jointed and some- 

 times divided into short irregular prisms, but which has no 

 slaty cleavage ; and with these slates are interstratified harder 

 beds of greywacke, which are occasionally conglomerate. 

 They are composed of felspar and quartz with a little mica 

 and sometimes chlorite. Their dip is always high but irregu- 

 lar both in amount and direction ; but though crushed and 

 squeezed, highly inclined and folding over each other, the 

 general strike of the beds is pretty regularly from north-west 

 to south-east. Strata of the same age and character abut 

 against the porphyry in Lambden burn near White Lee and in 

 the bed of the Reed near to Ramshope, whence they extend 

 up the Carter fell nearly to the Toll bar ; they are covered 

 unconformahly by beds of the mountain limestone era. These 

 greywacke strata are a prolongation into Northumberland of 

 the same system which runs across Berwickshire in a west- 

 south-west direction from Siccar point and Burnmouth, and 

 which occupies about one-third of Roxburghshire in elongated 

 ridges of moderate elevation. In a similar crushed and 

 elevated condition these greywacke beds abut against the 



