Natural History. 31 



still known. I hope to visit it this season. Can anyone give 

 me further fa&s about the late Mr. George Whitworth, and 

 supply me with specimens of his variety of L. perenne^ L. ? 



THE EDITOR. 



THE 'BLUE STONE' BOULDER, LOUTH, 

 LINCOLNSHIRE. 



By W. HAMPTON, F.C.S., Hanky, AND H. WALLIS KEW, F.E.S., Louth* 



THE Louth 'Blue Stone' is a subangular boulder of a 

 blue-black colour, about 32 inches in height and about 

 145 inches in girth, estimated to weigh from four to 

 five tons, which has existed in Louth for centuries, and now 

 rests in the yard of the c Blue Stone Printing Office ' in Mercer 

 Row. 



This boulder is, doubtless, a natural monolith of glacial 

 times ; its surface, however, does not exhibit definite striae. 

 Unfortunately, its natural position is unknown, but considering 

 its large size and great weight, the presumption is that it was 

 originally found in the immediate neighbourhood of Louth. 



After preparing and examining a large number of micro- 

 scopical sections, we consider the stone to be a typical Dolerite. 

 It consists of crystals of Plagioclase felspar (Labradorite) ; 

 Augite, very fresh and in large crystals ; Titaniferous Iron ; a 

 greenish-looking decomposition product (which may or may 

 not represent former Olivine) , and brownish stains, which 

 are probably due to the oxidation of the iron. As the result of 

 our examination did not exactly agree with the conclusions 

 arrived at by one who had previously examined the stone, a 

 section was submitted to Dr. Bonny, who says: 'The slide 

 contains Plagioclase felspar, probably Labrodite ; Augite ; 

 Iron Oxide (llmenite) ; and a greenish mineral of secondary 

 origin, probably indicating the former presence of a ferro- 

 magnesian-silicate. The replacing mineral is so indefinite in 

 its character that I can hardly venture to give it a name. The 

 structure of the rock is " Ophitic." It is merely a question 

 whether we should call the rock a dolerite or a diabase. It is 

 not a very typical diabase, but is a slightly altered dolerite. So 



* Reprinted from The Naturalist, 1887, pp. 225-226, by special permission. 



