liv. PRESIDENT'S ADDRESS. 



Exogens, like those of Endogens, consist only of cellular tissue, 

 and as soon as the leaves have fulfilled their functions, a circle of 

 fibro-vascular bundles is interposed between the pith and the 

 bark. At this stage the pith, wood, bark, and medullary rays 

 are seen in the stems of Exogenous herbaceous plants. The 

 veins of the leaves of Dicotyledonous plants are reticulated, the 

 sub-veins form a net- work throughout the entire substance of the 

 leaf, which affords it a degree of strength and firmness, and an 

 indisposition to split up or tear, an advantage which the leaves of 

 Monocotyledons do not possess. 



As we trace the history of mankind back to very ancient times, 

 we find that the records become more and more scanty and less 

 intelligible, until history fades into myth and tradition. Similarly, 

 among geological records the earliest are in such excessive 

 confusion, that they are very difficult to understand, and there 

 must have been an inconceivably long time earlier than the 

 most ancient fossil-records to which inference can be the only 

 resource. It is an unfortunate circumstance that historical geo- 

 logy should have to begin with the most obscure part of the 

 whole subject, and the chronology be most difficult to trace in- 

 telligibly. The ordinary criteria of stratigraphical succession 

 and the comparison of fossils fail us entirely, as the Archaean 

 rocks, which are the most ancient have yielded no evidences of 

 life. Their antiquity is best assured when they are separated by 

 thick series of sedimentary or metamorphic rocks from the Lower 

 Cambrian which can be identified by their fossils. There 

 is a conflict of opinion as to the origin of these primitive rocks, 

 but that they are igneous there is no doubt. Taking into con- 

 sideration the foldings and crushings which the earth's crust has 

 undergone, it is not surprising that they should have acquired 

 such a complex and intricate structure, and have been so 

 completely metamorphosed, that these transformed sediments 

 have possibly had all traces of their fossils entirely obliterated. 



The Palaeozoic is the oldest of the three main groups into 

 which the fossiliferous strata are divided. The thickness of this 

 group in Europe is 100,000 feet. The beds appear to have been 



