Rocks near Heathcote. 313 



In discussing the relations of the Heathoote rocks to the 

 Silurian, Prof. Gregory records fragments of diabase in the 

 matrix of the basal Silurian rocks of the Copper mine. This, 

 together with Lidgey's record of pebbles of metamorphic rock 

 in the Silurians, certainly indicates a pre-Silurian age for the 

 diabase and cherts. 



Tlie evidence which Prof. Gregory quotes of the relations of the 

 diabase to the Ordovician is of a less direct character. He 

 states that in places he found no evidence of alteration at the 

 contact. At Red Hill, where schistose rocks occur between the 

 diabase and unaltered Ordovician, he was unable to find either 

 a sharp junction or a passage from schists to Ordovician, but on 

 microscopio examiination was always able to say whether a rock 

 belonged to the schistose or to the Ordovician series. It seems 

 to me that these determinations under the microscope should be 

 interpreted ven* cautiously where the field evidence is not clear, 

 inasmuch as two sections cut from I'ocks of the same series might 

 easily present very different microscopio characters if one were 

 unaltered and the other highly altered. 



On p. 161 Prof. Gregory refers to Craven's paddock, in 

 Knowsley parish, allotment 32, where he says : " The two rocks 

 can be- well seen in contact close along the eastern fence. Here, 

 as elsewhere, the junction between the hard cherts of the meta- 

 morphic series and the normal slates and sandstones of the 

 Ordovician series can be clearly recognised." The statement 

 of locality is almost cei'tainly a misprint for Knowsley East, 

 as the diabase series does not occur in Knowsle}^ The name 

 of Craven does not appear on the map, and allotment 32 does 

 not occur along the line of the metamorphic or diabasic rocks. 

 The number of the allotment is probably wrongly stated, and 

 this is unfortunate, as Professor Gregory's statement implies the 

 occurrence of a discontinuity at this point between the cherts 

 and the normal Ordovician. 



Professor Gregory comments on the absence of dykes from 

 the igneous rocks intruding the Ordovician and Silurian rocks, 

 and regards this as imi>ortant negative evidence of the pre- 

 Ordovician age of the igneous rocks. He lays great stress on the 

 evidence afforded by the geological maps, which he claims is in- 

 consistent with the view of Air. Howitt that the igneous series is 



