328 ME. G. EARPvOW ON THE OCCURRENCE OF [Aug. I901 



25. On the Occurrence of Silurian [?] Eocks in Porfarshire and 

 Kincardineshire along the Eastern Border 0/ /7ie Highlands.* 

 By George Barrow, Esq., P.G.S. (Read May 22nd, 1901.) 



CONTE>'TS. -r. 



Page 



I. The Mode of Occurrence of the Rocks 328 



II. Their Lithological Characters and Order of Succession 328 



III. The Age of the Two Series 334 



lY. Tlie Kature of the Northern Boundary of the Silurian [?] 



Rocks ' 335 



Y. The Position of the Major Ihrust with reference to the 



Highland Rocks 339 



YI. The Mechanical Deformation of the Silurian [?] Rocks ... 342 

 YII. Summary of Results 342 



I. The Mode of Occurrence of the Eocks. 



Along the south-eastern border of the Highlands, between Blair- 

 gowrie and Stonehaven, a remarkable group of rocks has been 

 mapped in the course of the geological survey of that region. They 

 occur as isolated lenticular strips, which intervene between the 

 schistose rocks of the Highlands on the north-west and the boundary- 

 fault that truncates the Old Eed Sandstone on the south-east. The 

 first and largest of these lenticular strips is about 20 miles long, 

 extending almost from Cortachy in Forfarshire to about a mile 

 beyond the Clattering Bridge in Kincardineshire. In the valley 

 of the Xorth Esk it is about | mile broad, but elsewhere much 

 narrower. The second lenticular mass begins at a point about a mile 

 north of Drumtochty Castle, and stretches for 6 miles in a north- 

 easterly direction to the Braes of Bervie. Part of a third strip is 

 shown on the eastern margin of Sheet 66 of the 1-inch Geological 

 Survey Map of Scotland, on the north side of the Highland Fault. 

 The lenticular mode of occurrence of these rocks is due to the alter- 

 nate approximation and recession of their northern margin from 

 the great fault which everywhere forms their southern boundary. 



II. Their Lithological Characters and Order of Succession. 



Notwithstanding the mechanical deformation which these rocks 

 have more or less undergone, we are still able to ascertain their 

 original characters and mutual relations. They may be arranged 

 in two divisions, namely : — (1) the Jasper and Green-Eock Series ; 

 and (2) the younger Margie Series. 



Section in the North Esk Eiver. (Fig. 1, p. 330.) 



An almost complete section of the whole series is exposed in 

 the Xorth Esk, though parts are visible only when the riverjjis 

 low. Beginning at Gannochy Bridge, near Edzell, and proceeding 

 northward, we traverse an almost continuous section of Old Eed 



^ Communicated by permission of the Director of H.M. Geological Survey. 



