Wright— List of Irish Cretaceous Microzoa. 
75 
weight of the material. Chalk flints are usually found hard and solid through- 
out, only a small proportion of them having cavities containing Chalk powder. 
So far as I have observed, those containing the powder appear to be confined 
to flints that have, for some time, been exposed to the action of the weather, 
the white material frequently seen in the interior of those newly quarried being 
always of a hard nature. I have met with Chalk powder in every stage, from 
powder as fine as the finest flour, to a material so hard that it was difficult to • 
cut it with a penknife. The flints that contain powder may be readily known 
from the solid ones, by having openings from the outside varying much in size, 
the only trace at times being a little moss that has taken root on the chalky 
material exposed near the surface. It is not intended that the present list of 
Microzoa should be considered exhaustive, our knowledge of the contents of 
the flints in the North of Ireland is after all but very limited. Many localities 
in the northern parts of the Counties of Antrim and Londonderry have yet to 
be explored, whilst at several of the stations already examined the search for 
Chalk powder has been most cursory, and on several occasions only small 
samples of it were collected during hurried visits. 
The Cretaceous rocks of the North of Ireland are found invariably underlying 
the Basalt, and are usually well exposed at the base of those hills which occupy 
the boundary line between it and the sedimentary rocks. They occur as a 
narrow belt of White Limestone and Greensand around the great basaltic 
plateau which occupies nearly all Co. Antrim and the eastern part of v^o. Derry. 
I have given the localities for the Chalk Microzoa in the order in which they 
occur, commencing at Magheralin, the most south-westerly point examined ; and 
then, in a north-easterly direction, through Lisburn, Belfast, Carriclcfergus, 
Islandmagee, to Larne ; then, north and north-west, round the coast to the 
Giant’s Causeway ; then, inland, into Co. Londonderry, ending in the high 
escarpment of Slieve Gallion and Keady Hill. 
To my friend, Prof. T. Rupert Jones, F.R.S., I am deeply indebted for 
kind assistance rendered by him in the critical examination of my entire 
collection of Ostracoda and Foraminifera — an examination which has resulted 
in the detection of several new species. I am further indebted to Prof. J ones 
for names and references respecting all the forms here enumerated. Dr. J. S. 
Bowerbank, F.R.S., has also laid me under weighty obligations, by gener- 
ously undertaking to revise my whole series of Sponge spicula, a work of 
peculiar difficulty. His report on the spicula will be given in full. To my 
friends, Mr. William Gray, M.R.I.A., Mr. Samuel A. Stewart, F.B.S.E., and 
Mr. Thomas Galloway, I am indebted for kind and liberal assistance in 
procuring for examination a large amount of material from various localities. 
To the kindness and skill of my friend Mr. William Swanston I am much 
indebted for the very accurate drawings in the plates which accompany this 
memoir. 
