XIV PREFACE. 



early mineralogists and geologists also, appear to 

 have been satisfied with their own limited accounts 

 of the subjects of their researches. Yet we are 

 hardly able to refer with certainty to one object 

 in the descriptions of the former; and the obser- 

 vations of the latter scarcely enter at present as 

 a constituent into the science. The recent light 

 thrown on geology by the minute circumstances 

 which attend tne junctions of different classes of 

 rock and the passage of veins, are too well known 

 to require to be pointed out among the latest im- 

 provements in the mode of observation. 



It has also been imagined, that from thus mi- 

 nutely detailing some of these appearances, the 

 geological student, to whom practical investigations 

 are yet unknown, may derive rules for his guidance, 

 and, without the formality of instruction, receive hints 

 that may tend to shorten his labour and direct his 

 attention to those circumstances in the history of 

 rocks which appear to be the most important and 

 the most in need of illustration. 



I fear the reader will have reason to complain 

 that he cannot here discover any traces of a general 

 theory, nor sufficient references to past theories to 

 guide his steps through the multitude of details. 

 If he should also complain that disorder has been 

 introduced into a system which possesses, at least, 

 a respectable regularity, I can only say that the want 

 of coincidence between the present facts and our 

 systems, cannot be a greater cause x)f inconvenience 

 to him than it was to myself. The want of a theory 

 to which the observed appearances could be recon- 

 ciled, proved a constant source of difficulty, and of 



