1869.] ( 353 ) 



III. ON A TERNAEY GEOLOGICAL CLASSIFICATION. 



By Edward Hull, M.A., F.E.S. 



The views I am about to advance in the following paper are the 

 result of observation and reflection extending over several years, 

 at first somewhat vague, but now taking a definite form and direc- 

 tion. They are advanced with some diffidence, and I am aware 

 that exception will be taken to some of my conclusions as being 

 contrary to general acceptation. Such objections, as far as they 

 have occurred to myself, have been well weighed. It must be left 

 to time to determine whether there is sufficient ground for be- 

 lieving in a general law of development of geological formations, 

 depending on the mutual relations of organic and inorganic agencies ; 

 in the meanwhile I content myself with the endeavour to point out 

 the evidences of such a law as bearing more especially on the 

 arrangement of the British strata, leaving to a possible future the 

 attempt to deal with those of foreign countries. 



Tiie tendency of several groups of strata to assume a three- 

 fold arrangement has not escaped the notice of geologists. Sir 

 Koderick Murchison has very strongly insisted on it in reference to 

 the " Permian system," both in Britain and the Continent. The Trias 

 is (as its name denotes) an evident example, as is also the great 

 Carboniferous series both of Britain and America. In each of these 

 cases we have a central calcareous member interposed between an 

 upper and lower member composed of sandy or muddy materials, to 

 which the term " sedimentary " may be apphed. Now, when we 

 find in the case of three great groups following each other in order 

 of time, and lying on the margins of the grand divisional hne which 

 marks the boundary of the Palaeozoic and Mesozoic series, a similar 

 order of sequence and of mineral composition, we may well pause 

 and inquire whether there must not be some great principle lying 

 below the surface, impelhng or guiding the operations of nature 

 in the direction of geological cycles, reproducing themselves at 

 distant intervals, and indicated by the mineral characters of the 

 rocks. It may seem a hazardous assertion that the history of a 

 natural system (or group) of strata is analogous to that of a nation, 

 or of man himself individually ; that it has its beginning, its prime, 

 and its decline ; and that each of these stages has its representation. 

 Yet the evidence in favour of this view is very strong, and seems 

 to fall in with the course of physical events which we know to have 

 occurred at successive geological periods. This view of the natural 

 grouping of strata forced itself on my mind in 1862, when treating 

 in the pages of the ' Journal of the Geological Society of London ' 

 on the relative distribution of the " calcareous" and "sedimentary" 



