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Each system is distinguished in all maps and sections by the definitecolour or tint allotted to it in the schedule.

Formations.—These are the large systematic divisions actually inuse in describing the geology of New Zealand , being a naturalclassification of the stratified rocks, founded on observation. Eachformation is distinguished in the map, plan, or section, and whenreferred to in reports, by Roman numerals or capital letters, and bya distinctive marking impressed on the colour of the system to whichit belongs. As far as possible the names usually applied to theequivalents of these formations in other countries have been employed,for the convenience of those to whom local names are unfamiliar; butin several instances the natural subdivisions of the strata which admitof being mapped overlap the conventional subdivisions. In such cases,local or composite terms have been used, as, for instance, “ Waipara ”or “ Cretaceo -tertiary formation/’ which includes the Lower Eoceneand Upper Cretaceous of ordinary classifications, for the reason thatno division-line that can be used for the purpose of practical geologycan be interposed. The term “ formation ” is therefore to be read asthe local development in the New Zealand area of any system or partof a system the boundaries of which can be distinctly traced inmapping the country.

Series .—The terms “ series ” and “ beds ” are of use chiefly indescriptive geology, and can rarely be employed as distinguishingfeatures in general maps; but in local geological plans, and inillustrative sections, they are frequently introduced. Each series ispart of and subofdinato to a formation, and bears the name of thelocality where the most typical, or, in some cases, the first-discovered,section of the particular series of beds was found. Each series isindicated by an Arabic numeral following the number, letter, or nameof the formation in which it occurs. The division of any formationinto series is dictated entirely by practical utility. As far as possible,the different series adopted in the classification are arranged so as tobe consecutive in superposition and age, but in some cases the termhas necessarily been used in a descriptive sense.

The “ beds ” (layers or strata), in the particular application of theword, are the things to be classified under the foregoing phrases, andthis term is therefore of very v-aried application. As a rule the termis employed to indicate an irrfperfect and local development of aseries, or a portion of a series, that has well-marked distinctivecharacters, founded on its mineral composition or fossil contents.