UTRECHT MICROPALEONTOLOGICAL BUllETINS

Ordovician limestones of Sweden (1955a) and on bland (1963), and already
proved the suitability of these microfossils for detailed biozonation (1955a
and 1971).
From each of the rock-sections 1, 6 and 14, about 50 samples were used.
They were digested in 15% acetic acid solutions of 500-70°e. The limestone
samples were 100-200 gr., whilst those of the Djupvik Formation weighed
up to 1000 gr. After washing the residues, the fractions between SOil and
1.5 mm. were dried. Further isolation of the conodonts was attained by
using the magnetic properties of the anorganic constituents of the resid1±es.
The conodonts were concentrated by a magnetic separator in the a-magnetic
fraction. If separation by this method was insufficient, the conodonts were
afterwards isolated by treatment with bromoform of 2.87 specific gravity .•
All samples of the Kopingsklint Formation, the Bruddesta Formation, and
the Horns Udde Formation were usually rich in conodonts. Once 12.000
conodont specimens were calculated to be present in alSO gr. sample of the
Bruddesta Formation. By using a microsplit, a representative portion of the
total fauna was isolated and studied under binocular microscope. Finally,
approximately 300 conodont specimens were collected and determined from
each sample. To avoid selective collection of these 300 specimens, the
representative portions of the faunas were strewn in a tray with a lineated
bottom and the conodonts were searched systematically along the lines.
Charts II, III and IV show the distribution of the conodont species in the
rock-sections 1, 6 and 14, respectively. The distribution charts are composed
on the basis of the bottom method.
In every rock-section conodont assemblages were distinguished, mainly
using the first appearances of species. In some cases, however, the disappearance
of one or more species was used for zonal boundaries as well. The
assemblage zones of sections 1, 6 and 14 first got a preliminary notation.
After comparison of these three zonations every zone was given an official
name. The zonation was much facilitated by the presence of many discon-