224 



THE GEOLOGIST. 



the genera Bothriolepis, Asterolepis, Pteraspis, and Cephalaspis were dis- 

 cussed. 



3. " On Missing Sedimentary Formations from Suspension or Item oval 

 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 " Roof " 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 " Hoof," and drawing cer- 

 tain inferences from a consideration of them respecting the influence of 

 oscillation of level, emergence, denudation, etc., in their production. In 

 hi3 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 Paradoocides 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 cystidean — 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 Lancashire." 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 Rocks 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, 



