224 
THE GEOLOGIST. 
the genera Bothriolepis, Asterolepis, Pteraspis, and Cephalaspis were dis» 
cussed. 
3. " On Missing Sedimentary Formations from Suspension or Removal 
of Deposits, — their general relations and importance." By Dr. J. J. 
Bigsby. In this paper the author brought together nearly all the known 
instances of gaps or blanks in the stratigraphical succession in different 
countries. Of the two formations which are in apposition through the 
absence of one or more formations, which thus constitutes a blank, Dr. 
Bigsby applied the term "Boof " to the upper, and " Floor " to the lower. 
He then described briefly the principal instances, arranging them accord- 
ing to the age of the formation constituting the "Boof," and drawing cer- 
tain inferences from a consideration of them respecting the influence of 
oscillation of level, emergence, denudation, etc., in their production. In 
his concluding observations Dr. Bigsby observed that these gaps indicate 
that there always have been areas of dry land, and also showed that they 
prove the geological record to be, in places very much obscured, if not 
entirely obliterated. 
Geological Society. — March 23. — 1. " On some new Fossils from the 
Lingula-flags of Wales." By Mr. J. W. Salter. — Since the author's paper 
last session on the discovery of Paradoxides in Britain, the researches of 
Mr. Hicks have brought to light so many new members of the hitherto 
scanty fauna of the Primordial zone, that Mr. Salter was now enabled to 
describe two new genera of Trilobites, and a new genus of Sponge, and to 
complete the description of Paradoxides Davidis. He also remarked that 
the fauna of the Lingula-flags shows an approximation, in some of its ge- 
nera, to Lower Silurian forms, and some — the shells and a cystideau — are 
of genera common to both formations ; but the Crustacea, which are the 
surest indices of the age of Palaeozoic rocks, are of entirely distinct genera ; 
and their evidence quite outweighs that of the other fossils. The Primor- 
dial zone is, moreover, in Britain separated from the Caradoc and Llan- 
deilo beds by the whole of the Tremadoc group, at least 2000 feet thick. 
2. " On the Millstone-grit of North Staffordshire, and the adjoining parts 
of Derbyshire, Cheshire, and Lancasliire." By Mr. E. Hull and Mr. A. 
H. Green, — In this paper the Millstone-grit series was described, from the 
eastern edge of the Lancashire coal-field southwards to the coal-fields of 
North Staffordshire. After giving a general sketch of the geology of the 
district, and defining the upper and lower limits of the Millstone-grit, the 
authors explained a series of sections, running from east to west, at in- 
tervals across the country. In the most northerly of these the group 
consists of five thick gritstone-beds, separated by seams of shale, and 
attains a thickness of more than 2000 feet ; while on the extreme south 
all but two of these beds have thinned away, and the whole thickness is 
there not more than 300 or 400 feet. 
Between the base of the Millstone-grit and the Carboniferous limestone 
lies a group of shales and sandstones, with thin earthy limestones towards 
the bottom, which seem to hold the place of the Yoredale Bocks of York- 
shire. The mineral character of these beds was described, and their place 
noted on the sections. 
A short notice was also given of two small in-liers of Carboniferous 
limestone, namely, at Moxon, east of Leek, and st Astbury, near Con- 
gleton. 
Geological Society. — April 27. — 1. " On the Geology of Arisaig, 
