xiv. SUCCESSION OF LIFE-FORMS. 407 



leader in biology, now lost to science, conjectured ? To his mind 

 the more than usual introduction of new genera after the palaeozoic 

 ages presented that supposition, and he regarded the later periods 

 as to a certain extent strongly marked off, and called them Neozoic. 

 Previously, this seeming boundary, and another where the tertiaries 

 begin, had been generally recognized as important to separate the 

 palaeozoic, mesozoic, and cainozoic strata and systems of life. 



If so, if in the earlier periods of the world's life-history there 

 were epochs of uncommon genetic energy, this can only mean, 

 in the language of science, epochs when physical conditions in- 

 fluential on life-form or life-production were combined to be 

 exceptionally effective. What are these conditions? what were 

 those combinations ? Did they operate on the germ of life, or direct 

 its first development, or modify both function and structure at 

 every instant of its growth ? These are questions to which, perhaps, 

 we shall never be able to find satisfactory answers ; yet even such 

 hard problems must not be given up as desperate till we have 

 learned how much or how little may be done, and worked our way 

 toward a clearer view of the irremovable obstacle which must be 

 encountered at last. 



Life that transitory force seated among elements of matter 

 which itself selects and arranges ; stationary in currents of mole- 

 cular energy which it excites, directs, and renews; which is not 

 matter, nor the sum of the forces of the elements of matter, taken 

 in any proportions we please, and yet is known to us only in 

 material forms, during limited periods of time; forms which are 

 every moment undergoing variation, though composed of atoms 

 which are themselves exempt from change and independent of time 

 surely here is an agency beyond the scrutiny of the agent ; the 



' . . . alte terminus haerens ' 



of the philosophy of unalterable ' centres of force.' 



An interesting, and at the same time rather difficult, question 

 has presented itself of late years in relation to those peculiar beds 

 of the Bath oolite system known at the distant points of Stonesfield, 

 Collyweston, and Brandsby. Were the slaty strata of these three 

 localities deposited contemporaneously, or niay their remarkable 

 analogies both in structure and organic contents be understood as 

 due to similarity of local conditions, which occurred at different 

 points of time in different parts of the sea-bed ? 



