;m 



H. Cookseij Burton — Yellow Sands and Marl. 



of Magnesian Limestone ; this, however, is not the case, the Marl 

 Slate is here in its proper position above 'Yellow Sands', but 

 is itself overlain by later beds of 'Yellow Sands' separated by 

 thin beds of Magnesian Limestone. The correct section is shown in 

 Fig. 2. The uppermost bed of ' Yellow Sands ', No. 8, is very 

 compact and should rather be termed a Magnesian Limestone grit or 

 conglomerate ; it consists of large and small grains and pieces of more 

 compact ' Yellow Sands ' cemented into a solid rock by a dark- 

 yellow cement of magnesium and calcium carbonates ; it represents 

 the latest stage of the deposition of ' Yellow Sands ', and was 

 probably produced by 'Yellow Sands' being blown and otherwise 

 carried into water, in which the deposition of Magnesian Limestone 

 was proceeding. A local unconformity between the ' Yellow Sands ' 

 and Magnesian Limestone is therefore proved at this point. The 



Fig. 3. Fissures in the Magnesian Limestone containing Yellow Sands. Dotted 

 portion, Yellow Sands; shaded portion, Marl predominating; bedded 

 sand at X, Y, Z. Length of section, 15 feet; thickness of sand at X> 

 \\ feet ; cross-hatching, Brecciated Magnesian Limestone. 



occurrence of these beds of sand, Nos. 4, 6, and 8, above the Marl 

 Slate and also above certain beds of Magnesian Limestone proves 

 that the formation of ' Yellow Sands ' proceeded, perhaps inter- 

 mittently, during the deposition of the limestone ; thin beds of 

 'Yellow Sands', one inch thick, sometimes occur between the 

 bedding-planes of the limestone just above the Marl Slate, but they 

 rapidly thin out to nothing. 



4. "We will now discuss the last and most satisfactory explanation 

 of the occurrence of these secondary beds of 'Yellow Sands'. This 

 series, as has been shown by many writers, 1 is a great water-bearing 

 system, and is the source of the water-supply of Sunderland and most 



1 Professor Lebour, Trans. N. of England Inst. Min. Eng., vol. xxiv, p. 370, 

 1902-3. 



