OF HERTFORDSHIRE EOULDERS. 
49 
Asliwett (small boulder from gravel-pit, Clay Bush Sill, 2 ).—Yery 
much weathered throughout to a greenish-grey mass, showing 
crystals of pyroxene, olivine, and apparently mica. 
Beneath the microscope the felspar appears in well striated 
crystals of plagioclase, almost wholly filled, in parts, with the 
usual grey alteration-product. Augite appears to he the least 
altered mineral present. A notable feature is the unusually large 
amount of biotite, in strongly dichroic plates, with well-marked 
cleavage. Olivine was probably never very abundant, but is now 
almost entirely altered to fibrous, green, serpentinous pseudomorphs. 
Magnetite is not so plentiful as usual, and generally occurs in 
irregular patches, showing few characteristic square or triangular 
sections. Apatite is extremely abundant, and a few grains of 
quartz may be observed, evidently a secondary product. Green 
chloritic and brown ferruginous decomposition-products are scattered 
throughout the mass. 
Ashwell, 19.—No fresh fracture occurs in this specimen for 
macroscopic examination. 
TJnder the microscope the section appears much discoloured, and, 
in addition to triclinie felspar, augite, magnetite, and apatite, con¬ 
tains many large pseudomorphs of brownish-yellow and fibrous 
serpentinous matter, replacing the olivine. These pseudomorphs 
contain a great many magnetite enclosures, often arranged somewhat 
symmetrically, as in leucite and nepheline. There is also present 
a considerable quantity of a dingy-green, singly-refracting sub¬ 
stance (? chlorophceite). 
Ashwell, 103.—A very small specimen, much weathered. 
Under the microscope it is seen to contain triclinie felspar, much 
altered, and containing numerous crystals of apatite. The augite is 
faintly dichroic. Magnetite is abundant. The olivine is completely 
altered, and there is a great deal of secondary chloritic matter, with 
a little quartz. 
Kelshall, 1.-— This specimen is too much weathered and dis¬ 
coloured to give satisfactory results beneath the microscope. Its 
leading features, however, are somewhat similar to the above. 
Ashwell, 99.—A very small, weathered specimen. 
Under the microscope it appears much discoloured by reddish- 
brown ferruginous matter. Felspar (plagioclase) is fairly abundant, 
and augite, magnetite, and apatite occur as usual. The olivine is so 
completely altered as to be scarcely recognisable. A little biotite 
and a few grains of quartz may be recognised. 
Ashwell, 177. — Much decomposed throughout. Felspar is 
abundant', and augite, magnetite, and a little biotite occur. Apatite 
appears to be scarce, and olivine is not plentiful and is completely 
altered. A great deal of brown ferruginous matter discolours the 
rock. 
Ashwell, 26.—Much decomposed and discoloured. Felspar 
much altered. Olivine scarce and much altered. Magnetite, augite , 
and biotite occur. 
Hitchin , 2.—A dark crystalline rock, looking tolerably fresh. 
