Roc/,-f< near Heafhcote. 327 



s^een to be ooinposed of larirer and s-iualler anf;ular fragments of 

 diabase altered to a chloritic rock. Many fratrnients by the 

 introduction of silica in solution have been converted into cherty 

 rocks. The process of partial silicifieation has in the case of this 

 rock not been attended by the removal from the rock of its 

 original felspa.thic material. This has reorystallised as secondary 

 felspars, and with, them occur secondary quartz crystals. Irre- 

 gular chaleedonic areas are also to be seen, and small quartz 

 veins. The seconda,ry character of both the quartz and felspar 

 is indicated in places by the fact that the replacement of the 

 original diabase has bee^n only partially effected, so that the 

 secondary mineral has included some of the diabasic material. 



Flanking the foliated diabase of Tranter's paddock, M. of 

 W., Knowsley East, tliere is a bedded silicified rock mapped 

 as Ordovician. It occurs between tlie platy diabase and 

 the Ordovician shales, but its relations with each are not 

 clear, as no exposures are visible. Its bedded cliaracter 

 tends to link it ■with the sedimentary series, but its min- 

 eralogical constitution shows its relationship to the diabase 

 series. The hand specimen has a pitted surface, due to the 

 solution and renicval of minerals. The shapes of the cavities 

 are of two kinds, the one elongated prismatic, suggesting the 

 former presence of actinolite, the other clearl}'- having the shape 

 of felspar crystals. Under the microscope (No. 584) (PL XV., 

 Fig. 1) the bedded and cavernous characters are visible. Numerous 

 altered crystals of pyroxene and larger fragments of igneous rocks 

 are set in a fine textured groundmass, which is now silicified. 

 The rock appears to have been a bedded submarine tuff, or 

 possibly a clastic rock derived from a diabase shore line. A 

 precisely similar rock occurs flanking the diabase just W. of the 

 S. Heathcoto railway station, and some of the rocks in the area 

 mapped as Dinesus Beds are similar in character, and generally 

 more or less silicified. Under the description of the black cherts 

 I shall have to point out similarities which exist between many 

 of them and rocks of this character. 



The Granitic Rocks. — Dr. Howitt has given full petrolo- 

 gical descriptions of these rocks. One type he refers with some 

 hesitation to aplite, and notes that it is frequently granoph}Tic, 

 and the other he refers to as labrador-porphyrite. 



