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The N.Z. Journal of Science and Technology. [April 
shell which can with some degree of confidence be referred to the same 
as the Dun Mountain Inoceramus, as occurring between Cass and Bealey. 
I believe that indistinct fossils were also obtained at the time the road- 
cuttings were made along the Waimakariri, and both of these localities are 
no great distance from the one in the Hawdon Valley. The two records 
thus to some extent confirm each other. 
The other newly discovered fossil locality in Maitai rocks occurs in the 
Malvern Hills, at the old marble-quarry near the road from Whitecliffs to 
High Peak. A careful examination of the ash-beds associated with the 
marble discloses the presence on fracture surfaces of a sculpturing which 
closely resembles that on Monotis, as well as an occasional finer marking 
which may belong to Halohia. No calcareous material appears in con¬ 
nection therewith. The former of these identifications leaves little room 
for doubt as to its accuracy, whereas the latter is problematical. The 
occurrence thus corresponds exactly with that recorded by McKay from 
the Okuku district (Rep. Geol. Explor., 1883-84, p. 28), the similarity being 
not only in lithological character, as noted by Cox ( loc . cit., p. 28), but also 
extending to its fossil content. The marble, which occurs in discontinuous 
and irregular masses, has in all probability been formed by the recrystal¬ 
lization of the calcareous material contained in an ash-bed of Triassic age, 
either as an actual limestone or as shells scattered through a fragmentary 
volcanic deposit on an old sea-bottom. 
Note.— I have recently received from Mr. Koberts, roadman at Arthur’s 
Pass, per Mr. Charles Lindsay, assistant at the Canterbury Museum, a 
collection of fossils obtained from a metal-pit alongside the road on 
the Canterbury side of the pass, not very far from the summit. These 
include specimens of Pseudomonotis ochotica , Monotis salinaria, as well as 
other fossils. The matrix is a dark, slaty greywacke. Judging from the 
specimens submitted, it is very likely that a large number of examples may 
be forthcoming from this locality, and the roadman, who takes a keen 
interest in the matter, has promised to forward any others that he may 
come across to the Canterbury Museum. 
THE INTERPRETATION OF A TYPICAL SEISMOGRAM. 
By George Hogben. 
There has come into my hands, by the courtesy of Mr. Skey, Director of 
the Magnetic Observatory, the Christchurch record of the San Salvador 
earthquake of the 7th September, 1915—a particularly good record, which 
is reproduced in part as Plate I. I take this as a text for explaining some 
of the recent developments of the science of seismology. 
The diagram (Plate I) is from a tracing of the original photographic 
record, not modified in any way. The first waves, P, formerly called the 
“ first preliminary tremors,” are shown on the extreme left of the diagram ; 
their arrival at Christchurch is marked by a small but distinct jerk or impetus 
(hence, iP) at lh. 35 m. 42 s., Greenwich civil mean time, although a small 
swelling in the line at 1 h. 35 m. 00 s. (visible only through a magnifying- 
glass) may possibly indicate an earlier gradual beginning, or emersio (eP). 
The diagram is a typical Milne seismogram ; but it has this very remarkable 
