T. Mellard Reade — Keuper Marls at Great Crosby. 417 



of a rock which elsewhere contains a considerable quantity of felspar, 

 the one passing into the other in the same quarry, and almost 

 certainly in the same mass. In a classification it must be completely 

 separated from the peridotites, for it is related by composition, 

 on the one hand to the picrites, on the other to the olivine-dolerites, 

 and so occupies, whether in its glassy or holocrystalline condition, 

 a transitional position. Thus, if limburgite be restricted to the 

 vitreous type, a new name must be coined for the other one. It is, 

 however, I think, worth considering whether it would not suffice to 

 speak in future of Limburg-tachylite, Limburg-basalt, etc. 



V. — Another Section of Keuper Marls at Great Crosby, 



Lancashire. 

 By T. Mellard Reade, C.E., F.G.S., F.R.I. B.A. 



IN 1884 I described in the Geological Magazine a section of 

 Keuper Marls exposed by the excavation of the Boulder-clay 

 at Moorhey, Great Crosby.' This was our first knowledge of their 

 existence in the neighbourhood, the whole area being covered with 

 a thick mantle of Boulder-clay excepting where the Lower Keuper 

 Sandstone comes to the surface in the villages of Great and Little 

 Crosby. 



The Great Crosby Machine Brickworks Company in extending 

 their operations in Cooks Lane have sunk a well at the bottom 

 of their brick-pit, proving the Boulder-clay to be 35 feet thick 

 from the surface at this point. It is of a remarkably homogeneous 

 constitution and plastic character throughout down to the very base, 

 there being only a vein of sand 1 foot thick at about 3 feet from 

 the bottom. The most interesting result of the sinking is, however, 

 the discovery that it rests upon the Keuper Marls. These Marls 

 are of a bright blue colour and micaceous. From a personal 

 examination of the well I found that here the Boulder-clay rested 

 upon a well-defined surface of the marls which do not appear to be 

 worked up and mixed with the clay. The well had penetrated 

 6 feet of the Marls, which fail to show very regular bedding, but 

 appear to have a general dip to the south-east. A bed of more 

 gritty material was to be seen on one side of the well, which is 

 5 feet in diameter, but it became pinched out on the other side. 



At a distance of about 440 yards, in a direction 32° south-east, 

 the Lower Keuper Sandstone crops out near the Police Station, 

 so that there must exist between the two places a considerable 

 fault to which may be due the disturbed appearance of the Marls. 



It is the intention of Mr. Peters, the managing director of the 

 Company, to ultimately clear out the whole of the Boulder-clay 

 to the full depth over most of the area. It was in this Boulder-clay 

 that the celebrated " Gypsum Boulder of Great Crosby," weighing 

 18 tons, now erected in the village, was discovered at a depth of 

 about 20 feet from the surface.- 



» Dec. Ill, Vol. I, pp. 445-7. See also Q.J.G.S., 1885, vol. xli, p. 454. 

 - See " The Gypsum Boulder of Great Crosby": Proc. Liverpool Geol. Soc, 

 Sess. 1898-99, i^p. 347-356. 



DECADE IV. VOL. VUI. — NO. IX. 27 



