B. Thonqjson—FresIi-ivater Shells in the LincolmJdre Oolite. 223 



These facts appear to make it highly probable that alumina has 

 been eliminated ; but I wish, in concluding, to again point out that 

 the removal of this base is not vital to my general conclusion. 

 1 regard it as certain that the diorite has become highly acidic, 

 whether by combined elimination of bases and introduction of silica 

 or by elimination only. 



VII. — Peculiar Occurrence of Land and Fresh- water Shells in 



THE Lincolnshire Oolite. 



By Beebt Thompson, F.C.S., F.G.S. 



(With a page Section.) 



IN the latter part of 1893 Mr. Albert Wallis, of Brigstock, in 

 Northamptonshire, incidentally told me that he had found 

 some well-known land shells in the Lincolnshire Oolite at Brigstock. 

 The section from which these shells came I knew quite well, and 

 Mr. Wallis was well acquainted with recent shells, so it seemed 

 important to ascertain in what manner they found their way into 

 the Oolitic Beds. Having talked the matter over with my friend 

 Mr. Lionel E. Adams (Treasurer of the Conchological Society of 

 Great Britain), we decided to go over to Brigstock, and examine 

 the section and the shells, and arrive, if possible, at some explanation 

 of their peculiar position. Accordingly, on June 16 of last year, 

 we met Mr. Wallis there for the purpose indicated. 



The district in which Brigstock is situated has been described by 

 Prof. Judd ^ ; but in his Memoir two different sections are referred 

 to as at Brigstock Mill (see pp. 101, 149, and 191). That described 

 on page 149 is the one that we are concerned with, and is the one 

 to which the term Brigstock Mill most appropriately belongs, for it 

 is quite close to an old windmill, on the road towards Stanion, 

 i.e. on the north-west of Brigstock, and about a mile, or less, from 

 the village. 



The section Prof. Judd describes on pp. 101 and 191 of his 

 " Geology of Rutland," Lord Ly veden's pits, I find was commonly 

 known as the " brick-kilns," and is not now open ; it was situated 

 on the north side of the road just about half way between Brigstock 

 and Stanion. 



Description op Inferior Oolite Section at Brigstock Mill. 



1. The upper part of the section consists of soil, Boulder-clay, 

 and gravel. The Boulder-clay is scarcely distinguishable from the 

 soil above, except perhaps that it is a little redder and stiffer ; but 

 both contain very numerous pebbles and fragments of flint and 

 chalk, such as are usually found in the " drift " of the district. In 

 places the stones are so numerous as to almost constitute a gravel. 



2. Under the above, for a variable distance vertically, everything 

 is very confused — Boulder-clay, stones, fine sand, and shelly oolite 

 being very much mixed up, and consequently the junction with the 

 true Oolitic Beds below is very irregular. The thickness of this part 



1 " The Geology of Eutland," etc., by John "W. Judd. Memoirs of the Geological 

 Survey, 1875. 



