Professor J. E. Marr — Address. 407 



formation of the Olenellus beds, though their age has not been determined. 

 The Olenellus horizon now furnishes us with a datum-line from which 

 we can work backwards, and it is quite possible that the Neobolus beds 

 of the Salt Range, 1 which underlie beds holding 'Olenellus, really do 

 contain, as has been maintained, a fauna of date anterior to the formation 

 of the Olenellus beds ; and the same may be the case with the beds con- 

 taining the Protolenus fauna in Canada, 2 for this fauna is very different 

 from any known in the Olenellus beds, or at a higher horizon, though 

 Mr. G. F. Matthew, to whom geologists owe a great debt for his admirable 

 descriptions of the early fossils of the Canadian rocks speaks very 

 cautiously of the age of the beds containing Protolenus and its associates. 

 Notwithstanding our ignorance of pre-Cambrian faunas, valuable work 

 has recently been done in proving the existence of important groups of 

 stratified rocks deposited previously to the formation of the beds con- 

 taining the earliest known Cambrian fossils ; I may refer especially to 

 the proofs of the pre-Cambrian age of the Torridon Sandstone of North-west 

 Scotland lately furnished by the officers of the Geological Survey, and 

 their discovery that the maximum thickness of these strata is over 10,000 

 feet. 3 Amongst the sediments of this important system, more than one 

 fauna may be discovered, even if most of the strata were accumulated with 

 rapidity, and all geologists must hope that the officers of the Survey — who. 

 following Nicol, Lapworth, and others, have done so much to elucidate 

 the geological structure of the Scottish Highlands -may obtain the 

 legitimate reward of their labours, and definitely prove the occurrence 

 of rich faunas of pre-Cambrian age in the rocks of that region. 



But although we may look forward hopefully to the time when we may 

 lessen the imperfection of the records of early life upon the globe, even 

 the most hopeful cannot expect that record to be rendered perfect, or 

 that it will make any near approach' to perfection. The posterior segments 

 of the remarkable trilobite Mesonacis Vermontana are of a much more 

 delicate character than the anterior ones, and the resemblance of the spine 

 on the fifteenth "body-segment" of this species to the terminal spine of 

 Olenellus proper, suggests that in the latter subgenus posterior segments 

 of a purely membranous character may have existed, devoid of hard parts. 

 If this be so, the entire outer covering of the trilobites, at a period not 

 very remote from the end of pre-Cambrian times, may have been mem- 

 branous, and the same thing may have, occurred with the structures 

 analogous to the hard parts of organisms of other groups. Indeed, with 

 our present views as to development, we can scarcely suppose that 

 organisms acquired hard parts at a very early period of their existence, 

 and fauna after fauna may have occupied the globe, and disappeared, 

 leaving no trace of its existence, in which case we are not likely ever to 

 obtain definite knowledge of the characters of our earliest faunas, and the 

 biologist must not look to the geologist for direct information concerning 

 the dawn of life upon the earth. 



Proceeding now to a consideration of the faunas of the rocks formed 

 after pre-Cambrian times, a rough test of the imperfection of the record 

 may be made by examining the gaps which occur in the vertical distribution 

 of forms of life. If our knowledge of ancient faunas were very incomplete, 

 we ought to meet with many cases of recurrence of forms after their 

 apparent disappearance from intervening strata of considerable thickness, 

 and many such cases have actually been described by that eminent 



1 See F. Noetling, " On the Cambrian Formation of the Eastern Salt Range": 

 Records Geol. Survey India, vol. xxvii, p. 71- 



2 G. F. Matthew, " The Protolenus Fauna " : Trans. New York Acad, of 

 Science, 1895, vol. xiv, p. 101. 



3 Sir A. Geikie, " Annual Report of the Geological Survey [United Kingdom] . . . 

 for the year ending December 31, 1893." London, 1894. 



