R. Coofoey Burton — Yelloic Sands and Marl. 



303 



At Marsden large angular blocks of white chert, sometimes 9 inches 

 in diameter, have been found, and at Trow Kocks smaller pieces of 

 white and also black chert are met with. It is worthy of note that 

 this chert is always seen in the Middle Brecciated Magnesian Limestone ; 

 this, coupled with the facts above mentioned, proves that the chert is 

 of pre-Thrust age and probably contemporaneous with the limestone. 



2. The second suggestion is untenable, since the sand and marl 

 could not have been carried up during the movement of the rocks 

 caused by the thrusting, because the beds are quite undisturbed, 

 regularly bedded, and laminated ; moreover, the existence of false- 

 bedding in the sand points to deposition in water disturbed bv onlv 

 slight currents. 



3. At first sight this theory seems to be plausible, the more so 

 because at Tynemouth Cliff we find beds of 'Yellow Sands' above 

 the lower beds of Magnesian Limestone. Below is a sketch of the 

 Tynemouth Cliff section, showing the position of the later beds of 

 ' Yellow Sands '. 



W 



Brecciated 



MAGNESIAN 

 LIMESTONE 



Pig. 2. Section of Tynemouth Cliff. 1, Lowest bed of Yellow Sands, 12 feet ; 

 2, Marl Slate, 4 feet ; 3, Thin-bedded Magnesian Limestone ; 4, Yellow 

 Sands, 2 feet ; 5, Thin Magnesian Limestone ; 6, Yellow Sands, 3 inches ; 

 7, Thin Magnesian Limestone ; 8, Uppermost bed of Yellow Sands, \\ feet ; 

 9, Bedded Magnesian Limestone ; 10, Brecciated Magnesian Limestone, 

 20 feet. 



This section has been frequently misinterpreted ; in Sedgwick's paper 

 on the Geological Relations and Internal Structure of the Magnesian 

 Limestone l the Marl Slate is represented as overlying certain beds 

 1 Q.J.G.S., ser. II, vol. iii, pi. vi, fig. 1, 1835. 



