ME. A. STKAHAX ON THE LINCOLNSHIEB CAKSTONE. 489 



Section 6 is taken from the sinking journal of the shaft of the 

 Acre House Iron-mine. The iron-ore occurs at the base of the 

 Tealby Clay. The Carstone is described as resting directly on the 

 Tealby Limestone, the clay with iron-grains of the preceding section 

 being presumably absent. The reason of the thinness of the Spilsby 

 Sandstone is not clear; it preserves its usual thickness at the 

 outcrop close by. 



In Sections 5 and 4, the Carstone is highly conglomeratic, and 

 contains numerous nodules ranging up to three quarters of an inch 

 in diameter and imbedded in the usual ^gritty and clayey matrix. 

 In the lower part it is more sandy, but its base is concealed. 



North of this point there are no sections for some miles, but it 

 is known that the Carstone thins out within a short distance. 

 Eventually the whole Neocomian Series thins out and is overlapped, 

 the last section occurring near Audleby (No. 3). The Eed Chalk 

 here comes close down on to the Tealby Limestone, though there is 

 no actual exposure of the junction. Between the two there occur 

 phosphatic nodules similar to those found in the Carstone. 



From Audleby northwards the Red Chalk rests on Kimeridge 

 Clay as far as Melton Ross (about six miles), where the Spilsby 

 Sandstone reappears for a short distance (Section No. 2). The 

 base of the Red Chalk here is highly conglomeratic. In addition to 

 the usual quartz-grains, it contains abundance of the phosphatic 

 nodules so common in the Carstone. 



Section 1 is taken in the last exposure of Neocomian beds in 

 Lincolnshire. The Red Chalk passes down into a band of yellowish 

 or greenish clayey grit, containing phosphatic nodules and pre- 

 senting all the characters of true Carstone, except in its thickness, 

 which amounts to only two inches ; it rests with a marked 

 unconformity on the Tealby Clay. In a few yards' distance the 

 Neocomian rocks are entirely overlapped. 



Where they reappear in Yorkshire they consist of a series of 

 nearly homogeneous clays known as the Speeton Series, and divisible 

 into Upper, Middle, and Lower Neocomian by the fossils *. There 

 are no sandstones at Speeton corresponding to the Carstone or 

 Spilsby Sandstone t, but the latter may be correlated with the lower 

 part of the clay by fossils, as shown by Prof. Judd. 



It will be seen from the foregoing sections that the Carstone is 

 persistent, while the underlying Neocomian rocks thin from 261 

 feet to 47 feet. The disappearance of the Carstone appears to be 

 due merely to a similar thinning away in the same direction. This 

 northerly attenuation is shared also not only by the Red Chalk, but 

 by many of the Secondary rocks as -far down as the Lias. The 



* Judd, " On the Speeton Clay," Quart. Journ. Geol. Soc. vol. xxiv. p. 218 

 (1868). 



t It should be mentioned, however, that near Kirkby Underdale, in Yorkshire, 

 there occurs for a short distance at the base of the Chalk a very ferruginous 

 gritty sand, which, from its resemblance to beds of Neocomian age in Lincoln- 

 shire, has been classed in this division. Blake, Geol. Mag. dec. ii. vol. i. p. 363, 

 and Proc. Geol. Assoc, vol. v. p. 246 ; and ' Geology of the Country North-east of 

 York and South of Malton' (Geol. Survey Memoir), p. 25 (1884). 



