HuTTON. — On tlic Ages of the N.Z. Coalfiekh. 37& 



sition is occasionally very useful in the case of rocks of excep- 

 tional composition, such as red sandstones with gypsuin ; but 

 even here it can only be applied with caution, and in restricted 

 areas. It is a test which decreases in value as tlie formations 

 compared increase in distance ; and when the localities are 

 more than fifty miles apart this kind of evidence is usually of 

 very little weight, especially with the younger rocks, which 

 are rarely widely sj)read. We know that very dissimilar rocks 

 are now forming round our coasts ; we know that one kind 

 of rock can often be traced horizontally into another of quite 

 different mineralogical composition ; and we also know that 

 rocks of similar mineral composition have been formed at very 

 different periods of time : consequently lithological evidence 

 has always given way to palseontological evidence whenever 

 they have been opposed — as, for example, with the Old 

 and New Eed Sandstones of Britain, which were at first 

 considered as one from similar mineralogical composition, but 

 proved by fossils to be separated by the whole of the Carboni- 

 ferous period, this pala^ontological evidence being subse- 

 quently confirmed by stratigraphy. In the absence of all 

 other evidence mineral composition is our only guide, untrust- 

 worthy though it be ; and in the Highlands of Scotland it has 

 defeated the first efforts of stratigraphy. This, however, was 

 with Archaean and Palaeozoic rocks, and even here it was 

 palaeontology that really overthrew the old stratigraphy. 



Bearing in mind, then, the relative values of these three 

 kinds of evidence, we come now to the consideration of the 

 case of the New Zealand coalfields drawn up by Mr. McKay, 

 which will be found on page 55 of the " Eeports of Geological 

 Explorations " for 1887-88. Mr. McKay says " that the diffi- 

 culty is mainly a palffiontological one, and that if it were not 

 for the seemingly contradictory evidence afforded by the fossil- 

 collections from different localities, it does not seem that most 

 geologists would doubt the propriety of grouping the coal- 

 bearing beds at various places as the same or equivalent 

 developments of one formation, or of including as part of the 

 same sequence the fossiliferous marine strata that in most 

 cases overlie the coal-bearing beds." Now, I can quite agree 

 with Mr. McKay that if the same fauna had been found over 

 the coal at the different localities there would be no great 

 difficulty in considering the coals as all belonging to one for- 

 mation ; but I differ from Mr. McKay in thinking that, as the 

 faunas differ at different localities, there is no difficulty at all 

 in considering them as belonging to more than one formation. 

 I will state the case thus : — • 



It is a fact admitted by all that the fossils found in the 

 ))eds immediately over the coal at Waipara, Malvern Hills, 

 and Shag Point (which I will call the Waipara fauna) are 



