On the Rocks of the Essex Drift. 283 



difficult both to get a really representative collection and to classify 

 them when they have been collected. About two hundred speci- 

 mens have been taken, and sections have been made of one hundred 

 and fifty of these. There is a remarkable absence of granite of any 

 kind, and only two specimens of syenite have been found. Quartz- 

 porphyrites and quartz-tourmaline rocks are fairly abundant, felsites 

 are rarely met with, but felspar porphyrites are very abundant ; 

 trachytes also are found, but there is some reason for suspecting that 

 these do not really belong to the drift, but have been imported in 

 very early times. The most abundant of the igneous rocks are the 

 dolerites ; but all the coarser dolerites and those of a true ophitic 

 character are wanting. Many of the specimens are of subophitic 

 texture, and bear a general likeness to the subophitic dolerites of 

 Central England, though without having any special points of re- 

 semblance ; some of the specimens, however, are strikingly like the 

 rocks of the Whin- Sill, and that too in certain special points. The 

 dolerites of trachytic texture, or basalts, do not at all resemble 

 those of the North of England, but some of them are almost iden- 

 tical with certain Scandinavian basalts. One or two specimens 

 deserve special mention, and among them a hypersthene-bearing 

 dolerite that is more nearly ophitic than any of the others. Two 

 specimens of granulite containing hypersthene are interesting as 

 belonging to a well-characterized type. The crystalline schists are 

 not abundant ; among them is a hornblende schist containing abun- 

 dance of tourmaline. The sandstones, some of which are of very 

 large size, belong chiefly to the Carboniferous series, and, as a rule 

 are unfossiliferous. Two blocks, however, of fossiliferous sandstone 

 of a somewhat peculiar character have been found, and have been 

 identified with the sandstone of the Lower Neocomian series in 

 Lincolnshire. Of the limestones there are a great number of blocks 

 of a hard grey crystalline limestone of the Carboniferous series 

 containing some very perfect specimens of Foraminifera ; and 

 two specimens from the Rhaetic beds, which are of peculiar in- 

 terest if, as it is said, the Rhsetic beds do not now come to the 

 surface anywhere in the North of England. The greater num- 

 ber, however, of the limestones belong to the Jurassic series ; 

 there are also many lumps of very hard chalk which have been 

 identified with the hard chalk of Cambridgeshire. The micro- 

 scopic sections of the Chalky Boulder-clay show that amid grains of 

 quartz, sand &c. there are a great number of minute Poraminifera 

 still wonderfully well preserved. The way in which the Chalky 

 Boulder-clay and the gravels lie was well shown in a railway-cutting 

 near Dunmow some short time ago, and happily a small photograph 

 of the section was taken at the time, for that part of the cutting has 

 now been covered in. This investigation cannot be said, so far, to 

 have been productive of any great results ; but it is possible that 

 this attempt at classifying and describing the rocks of the drift may 

 be of some assistance to those who are considering the general ques- 

 tion of the glacial drift. 



