164 Transactions.— Miscellaneous. 
best “blue Bangor ;”’ and when similarly grained specimens of the two 
kinds are placed together, the best judge can searcely distinguish them. 
Captain Hutton informs me that there is a considerable difference 
between the cleavage of the Otago and English slate ; instead of ‘being at 
an angle to the strata, it is parallel to them. He points this out as a 
probable defect in the colonial article, but at the same time states that the 
property of splitting readily is not due to lamination but cleavage, conse- 
quently the pressure that gave this property must have been applied ina 
vertical rather than a horizontal direction. Without venturing to express 
an opinion on such an important geological question, it seems to me that = 
the idea of a regular vertical pressure, induced or aided by attraction of 
gravity, is more natural than a horizontal one; not only is the pressure 
abnormal, but we must pre-suppose the existence of a solid mould which 
prevented the lateral extension of the material. 
The roofing slates in England are all extracted from beds with inclined — 
cleavage ; and those taken from a horizontal stratum, where the angle of 
the cleavage planes is greatest, are supposed to be the readiest split, and 
otherwise the best ; but I do not know that there is a sound reason for this 
conclusion ; and although roofing slate has not hitherto been obtained from 
strata with a parallel cleavage, the existence of a cleavage of this kind in 
the clay-state formation is well known. Professor Geikie says, ‘‘ Cleavage 
may either coincide with the original lamination of the rock, or cut across 
it at an angle;” it is, therefore, possible that the exception in the old 
country is the rule at the Antipodes. 
_ Under any circumstance, the question cannot affect the industrial 
importance of the Otago slate; while we are satisfied that it splits freely, 
and is durable and impervious, its geological peculiarities may be dis- 
regarded. 
Tn addition to roofing material, slate quarries yield slabs for paving, 
hearths, mantel-pieces, and other works of a similar kind; the finer sorts 
are usually too smooth and soft for street pavements, but I have no doubt 
varieties suitable for this purpose will be found in the same locality. 
Following the plan adopted with the other materials, I shall devote a 
few remarks to the consideration of the comparative cost of slate and its 
principal sustitute, corrugated iron. 
Tt is popularly supposed that there is a great difference in the cost ; but 
such is not the case. Having occasion lately to decide on a covering for my 
own house, I calculated the difference carefully, and found that with Countess 
slates at £15 per thousand, and galvanised iron at £87 per ton, which are 
about the current retail prices, the cost of the two matérials was identical 
for the same space of roof. There is, however, a difference in favour of the 
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