Gudex. — Succession of Tertiary Beds in Pareora District. 249 



throughout South Canterbury and North Otago, so that they are easily 

 recognized. A few pectens and oysters are almost the only molluscs to 

 be seen in the marls, but the numerous concretions which these contain 

 enclose several species of molluscs, in addition to sharks' teeth and crabs. 

 These lower marls are rather coarse, suggesting that they were formed 

 not far from the old shore-line. Petrified wood and fossil amber are found 

 in these beds as well as in the lower sands and sandstones. The distinction 

 between these and the lower sands and sandstones is an artificial one, as the 

 one set of beds grades into the other. 



The overlying marls are almost unfossiliferous, probably because the sea 

 was becoming too deep for the shell-fish that had existed in the earlier 

 periods when the beds were laid down in comparatively shallow water. 

 They are transition beds, which were formed before the deep-sea fauna 

 could take possession of its new territory. The first of the new colonists 

 were crinoids, and later came molluscs, such as Atrina and some pectens, 

 together with echinoids and brachiopods. In the western part of the 

 district these marls pass up into a chalky limestone ; farther east the 

 marls pass up directly into a dark limestone. 



The Liv test one. 



This is an arenaceous limestone which passes upwards into clays and 

 downwards into marls. Its colour varies from yellowish to greenish-white, 

 owing to iron-stains and glauconitic sand. In some places near the old 

 shore-line the surface of the limestone is dotted over with black spherules 

 of ferric oxide, and sometimes small quartz pebbles may be found. It is 

 possible that these pebbles were carried out from the shore by clumps 

 of seaweed. The limestone is nearly always divided into hard and soft 

 layers, which in weathering give the rock a characteristic fluted appear- 

 ance. (See Plate XVI. fig. 1.) Followed eastward the rock becomes less 

 arenaceous, and more compact and siliceous, especially in the upper layers. 

 We find, too, that the thickness of the limestone has increased from 55 ft. to 

 100 ft. At the bottom of the ordinary stone there is a darker and more 

 arenaceous bed which contains many brachiopods, in addition to large 

 lamellibranchs, such as Pecten huttoni (Park), Lima laevigata Hutt., Lima 

 (Acesta) imitata Sut. Sharks' teeth are common in this layer, but only a 

 few are scattered through the upper part of the limestone. Sometimes the 

 lamellibranchs are so numerous as to define a joint-plane : thus a fallen 

 block may sometimes show hundreds of shells lying in the one plane. 



Beneath this dark layer there is sometimes a fine-grained chalky lime- 

 stone in which there are no traces of fossils. The whole of the main lime- 

 stone is glauconitic, but this character is best seen in the lower (dark) band. 

 Not only is the limestone thicker in all the areas remote from the old coast- 

 line, but the change from limestone to marl is much more definite. There 

 are numerous caves, which sometimes contain bones of extinct birds, such 

 as Harpagornis, Gnemiornis, and Dinornis. A noteworthy feature of the 

 weathering of the limestone is the tendency of solution to form deep, well- 

 like shafts. In one place I noted as manv as thirteen within an area of 

 less than 20 acres. (See Plate XVI, fig. 2.)' 



The uppermost layer of limestone, passing into the blue clay, when 

 examined microscopically is seen to be of very even texture, with a base 

 of some argillaceous substance. Globigerina tests, and round bodies that 

 are probably the detached chambers of Globigerina. are scattered all 

 through the rock. These are sometimes replaced by an iron compound. 



