INTRODUCTION. 



11 



the transition from a submarine condition, into the sera when the newly-raised surface 

 was first occupied by lakes and broad rivers. He will, in short, be conducted, step by 

 step, from the time when large portions of our island were beneath the sea, to the con- 

 sideration of the deposits which are in actual progress of formation above it j and thus 

 he will embrace in one view the passage from the vast geological epochs into the com- 

 paratively brief period of history. 



The first part of the work, including the descriptive geology of the region, will then 

 be terminated, by a review of some striking results of the present inquiry. 



The second part is exclusively devoted to Zoology, and contains the evidences on 

 which many of the principal conclusions are founded ; being a description of all the 

 fossils of the Old Red and Silurian Rocks, prefaced by a general view of the distribution 

 of animal life during the accumulation of those ancient strata. 



Geologists will determine whether the results now offered to them are worthy of their 

 approval. If it be acknowledged, that no sound general views of the early periods 

 of the earth's history can be obtained, without a close investigation of the beds which 

 connect the sedimentary deposits previously known with the oldest stratified rocks, then 

 I may venture to hope, that the endeavour to clear up this difficult subject, will be 

 considered a step, however small, in the foundation of the science. 



We already know, that certain deposits with their organic remains, maybe expected 

 to show themselves (though sometimes under different aspects) in distant lands. 

 Thus the tertiary and secondary strata have been identified over remote parts j 

 while our own island is remarkable for having afforded in great measure the original 

 types of the secondary age which directed that investigation. It appears highly pro- 

 bable, nay, it is even to a great extent already ascertained, that phenomena of the same 

 kind prevail with respect to the system described in this volume ; and that Siluria, with 

 its accumulations of remote antiquity teeming with organic remains, presents a table 

 made up of some of the earlier and hitherto undeciphered pages, which the history of 

 the earth in other countries offers to our study. 



But the Silurian, though ancient, are not, as before stated, the most ancient fossili- 

 ferous strata. They are in truth but the upper portion of a succession of early de- 

 posits which it may hereafter be found necessary to describe under one comprehensive 

 name. For this purpose I venture to suggest the term " Protozoic Rocks," thereby 

 to imply the first or lowest formations in which animals or vegetables appear. 



That there is a limit in the descending scale of formations, beneath which no traces 

 of life have been discovered, is now pretty generally recognised ; and looking merely to 

 this fact, geologists may agree to use the word " Protozoic," however they may differ 

 in their interpretation of the phenomenon. 



One class of observers believe, that life did not exist when the earliest deposits took 

 place. They hold that the oldest crystalline strata (ancient gneiss, mica schist, &c.) 

 were formed during a period of great heat : and the astronomer seems to strengthen 



