Thomson. — Geology of Middle Waipara and Weka Pass District. 389 



within eacli district a given species has been collected from. Part of this 

 analysis, applying to the species from the Waipara - Weka Pass district, is 

 given below in Table V. 



One immediate advantage of such a list is that it shows clearly which 

 species are based on single or few records, suggesting, in such cases as that, 

 for example, where a Recent species is recorded from the Waiarekan and 

 no higher stage, that the specimens are in need of critical re-examination 

 before this evidence for the range of the species can be fully admitted. 



A striking feature of the lists is the number of species which range 

 throughout the Oamaruian, and the comparatively few, except in the case 

 of the Awamoan, which are confined to a single stage. The reason for the 

 latter is that the majority of the good fossil-localities are Awamoan — viz., 

 Awamoa, Target Grully, Ardgowan, Otiake, Pukeuri, Mount Harris, Blue- 

 cliffs, Pareora River, White Rock River, Holme Station, Sutherland's, and 

 Kakahu River. The only large lists from the Waiarekan are from Black 

 Point (where the fossils are nearly all casts), Wharekuri, Waihao greensands, 

 and Kakahu coal-beds. I directed most of my collecting to Waiarekan 

 localities, in order to redress the balance ; but the results are still scanty 

 compared with the Awamoan, and as a result the use of the analysis for 

 comparison of fresh lists will tend to favour correlation with the Awamoan, 

 as will be seen below. 



The percentages of Recent species in the total faunas of the province 

 may be estimated in two ways — viz., by actual records, or by implication : 

 i.e., if a species in the Waiarekan is also known from the Awamoan or 

 Recent it may be credited to the mtermediate rocks. The numbers of 

 species and percentages of Recent species are as follows : By actual records 

 — Waiarekan, 221 (Recent, 56 = 25 per cent.) ; Ototaran, 90 (Recent, 28 

 = 31 per cent.) ; Hutchinsonian, 97 (Recent, 36 = 37 per cent.) ; Awamoan, 

 336 (Recent, 113 = 34 per cent.) : by implication — Ototaran, 178 (Recent, 

 69 = 39 per cent.) ; Hutchinsonian, 207 (Recent, 82 = 40 per cent.) ; 

 Awamoan, 347 (Receilt, 137 = 39 per cent.). It is to be expected that 

 when the collections from the lower stages are as exhaustive as those from 

 the Awamoan the percentages obtained by the two methods will approach 

 one another more nearly, and also that there will be a regular increase 

 from the Waiarekan to the Awamoan. It would be premature to assume 

 that there had been a sudden introduction of new forms in the Awamoan, 

 although that is the actual suggestion of the lists. 



To ascertain the evidence presented by a fresh list from any locality, 

 the best method appears to be to calculate the percentages of records in 

 each stage of the species in the new list. A somewhat similar method was 

 used by Marshall in 1919. If the analysed list is extended to include the 

 stages older and yoimger than the Oamaruian, then for any given fresh 

 list a series of percentages for each stage may be calculated which will rise 

 to a maximum for the stage to which the list belongs. The nearer this 

 maximum approaches 100 per cent, the higher the probability will become 

 that the correlation is correct. The percentage of Recent species will fall 

 into its place as only one of a series of percentages. At present, how- 

 ever, owing to the fact that the faunas of the various stages are so incom- 

 pletely known, and that the fuller knowledge of the Awamoan faima gives 

 proportionately higher percentages for that stage, greater weight than will 

 later be necessary must be attached meanwhile to the percentage of Recent 

 species. 



Applying the above method to the Wangaloa and Hampden faunas, 

 we get the following percentages (using the method of implication) : — ■ 



