(2.) Hutchinsonian Beds.
The Hutchinsonian is subdivided lithologically, in descending order, into—(a) Glauconitic sandstone (Upper Hutchinsonian); (b) Glauconitic greensands (Lower Hutchinsonian); (c) Conglomerate, mainly basaltic.
The glauconitic sandstone (a) is said to represent the Waitaki stone of Upper Hutchinsonian age. He describes this horizon as follows: “The glauconitic sandstone follows the greensands conformably… it consists of soft glauconitic sandstone interbedded with hard yellowish brown sandstone bands… it is a compact yellowish-brown calcareous
glauconitic sandstone.” The glauconitic greensands (Lower Hutchinsonian) are described in the following extracts: “The glauconitic sandy beds at All Day Bay, Kakanui, Hutchinson's Quarry, and Grant's Creek are loose and incoherent, but at the upper end of Target Gully, at Landon Creek, and in the Waitaki area they form fairly compact glauconitic sandstones” (p. 78). Further, it is stated that “the fauna of this horizon [Lower Hutchinsonian] is distinguished by the abundance of the brachiopod Pachymagas parki (Hutt.), by the presence of the corals Isis dactyla Ten.-Woods and Mopsea hamiltoni (Thomson), and of the cup-shaped bryozoan Celleporaria nummularia Busk. Besides these there occur many pectens and other molluscs. Pachymagas parki (Hutt.) is present almost everywhere, but the other fossils mentioned may be abundant at one place and absent at another” (p. 78). “Pachymagas parki (Hutt.) occurs in great abundance in the Lower Hutchinsonian, usually to the exclusion of all other brachiopods except Rhizothyris rhizoida (Hutt.), which is nearly always present with it” (p. 109). “The Lower Hutchinsonian is the most distinctive and persistent horizon of the Oamaruian system; it always overlies the Oamaru stone. In the Oamaru area it consists of calcareous glauconitic greensands that at Landon Creek and the lower Waitaki Valley are partly or wholly replaced by calcareous glauconitic sandstone. But whether greensands or glauconitic sandstone, the characteristic brachiopod Pachymagas parki (Hutt.) and the peculiar corals Isis dactyla Ten.-Woods and Mopsea hamiltoni (Thomson) are always present. The Waitaki stone is underlain by the greensands” (p. 110).
It will be shown that these sandstone bands in the Landon Creek area are referred to the Upper Hutchinsonian, although from Park's description of the characteristic fossils they should belong to his Lower Hutchinsonian (Hutchinsonian of Thomson).
As pointed out by the present writer (1916, pp. 20–21), the fossil Pachymagas parki (Hutt.) occurs in abundance in a well-defined band of hard glauconitic sandstone. In the present paper this band is called the “parki” band. It is ofter accompanied by Rhizothyris rhizoida (Hutt.), to the exclusion of all other brachiopods. This hardened band is underlain in many places in the district by looser greensands, also glauconitic, but characterized also by a constant assemblage of fossils—Aetheia gaulteri (Morris), Terebratulina suessi (Hutt.), Isis dactyla Ten.-Woods, and Mopsea hamiltoni (Thomson), which are all very abundant. This bed usually contains many specimens of Pachymagas parki (Hutt.), but in these looser greensands the individuals of this species are on the average distinctly smaller than in the upper “parki” band, and their external characters are far more constant. In the hardened upper band, where it is usually accompanied by Rhizothyris rhizoida (Hutt.), the specimens assigned to the “parki” species are extremely variable in external shape. As pointed out by Park in the extracts quoted, above, this greensand horizon is a most distinctive one; it is, the typical Hutchinsonian of the Oamaru system, and always lies above a nodular band (Park's conglomerate). Park, however, would term these “Isis” greensands, and the “parki” greensands Lower Hutchinsonian; and states that they are separated from the Awamoan by the Upper Hutchinsonian (Waitaki stone). The writer contends that the “Isis” greensands and the overlying “parki” greensands constitute the Hutchinsonian, and are followed directly by the Awamoan beds.
In the localities discussed below an attempt is made to show that where the Awamoan beds are present, as in the Oamaru area, the hard calcareous bands at their base are called Upper Hutchinsonian; where the Awamoan beds are not present, as at Landon Creek (west branch), the “fairly compact glauconitic sandstone” (the “parki” band) is called Upper Hutchinsonian; where the “parki” band is absent, as in Landon Creek (Papakaio district), the upper glauconitic portion of the limestone is called Upper Hutchinsonian (p. 64). The various localities in which the post-Ototaran beds occur will now be discussed.