368 Mr. George Tate on the Chemots. 



no rolled grains, such as make up sedimentary rocks, enter 

 into their composition ; nor are any planes of stratification to 

 he seen. Jointed they are, both vertically and horizontally ; 

 and some joints when viewed in section simulate the appear- 

 ance of strata ; hut when examined closely they prove to be 

 oblique joints, which, as well as the other joints, had been 

 produced by shrinkage when the rock was passing from a 

 molten to a consolidated state. 



Age. 



We are now more able to determine the age of the Cheviot 

 range. There have been at least two upheavals, the one 

 following the other after a long lapse of ages. The first pro- 

 trusion took place subsequently to the Cambro-Silurian era ; 

 for rocks of that age, which had originally been mud beds de- 

 posited in the sea in a nearly horizontal position, are highly 

 tilted up against the porphyry, by the protrusion of which, 

 the relative position had been altered. Within certain limits 

 we can also determine how long after that era this first pro- 

 trusion took place ; for, as pebbles of Cheviot porphyry form 

 part of the upper old red sandstone conglomerate, it is evident 

 that the Cheviots were elevated before that era. The tumul- 

 tuous waves of a shallow estuary broke over the lower portion 

 of the Cheviot hills and detached several blocks, and rolled 

 them, and heaped them in irregular beds, at a time when 

 ganoid fish swam in the waters, and ferns and probably 

 sigillarise grew on their slopes. Of the precise time of the 

 protrusion in the interval between these two eras we have 

 not evidence ; for our rocky records are here imperfect, there 

 being no trace along the flanks of the Cheviots either of un- 

 doubted lower Silurian, or of the upper Silurian, or of the 

 true Devonian systems. 



A second upheaval took place subsequently to the Tuedian 

 era, and probably not long after ; for beds of that age are 

 highly tilted up against the porphyry and syeniteboth in Akeld 

 burn and on the Coquet. Prior to this elevation the range was 

 submerged fully 900 feet below the present level, as is evi- 

 denced by the Tuedian blocks high up on the hills ', but sub- 

 sequently to this second protrusion, vast masses of strata must 

 have been removed by denudation on the northern and east- 

 ern sides of the Cheviot range. 



Botanical Peculiarities. 

 As the flora of a district is to a certain extent influenced 

 by the character of the rocks beneath the surface, some slight 

 notes may be added on the botany of the Cheviots. 



