1 84 THE JOURNAL OF GEOLOGY. 



The rocks of igneous origin, although sometimes interstratified 

 with sedimentary rocks, do not enter into the present geological 

 time -scale, and for the present purpose further consideration of 

 their classification is unnecessary. There has always been a 

 remnant of rocks at the base of the scale, the consideration of 

 which may be discarded here, because it is known chronologically 

 only as below those rocks of which distinct evidence of their 

 relative age is apparent. The name Primitive has been changed 

 to Primary, and finally to Archaean, a name which was proposed 

 by Dana, and is likely to be retained for some of the basal part 

 of the series. 



This first comprehensive classification of rocks may be called 

 the Lehmann classification. It was based upon a structural analysis 

 of the rocks in the order of their actual positions. The nomen- 

 clature is applied on the theory of relative order of formation. 



Richard Kirwan (Geological Essays, London, 1799), claimed 

 to be the first author to publish a general treatise on Geol- 

 ogy in the English language. Although the book is written 

 in a decidedly controversial spirit, the author appears to have 

 had a thorough acquaintance with the various treatises in French, 

 German, Latin and English, in which were expressed contem- 

 poraneous opinions regarding geological science. He was a Fel- 

 low of the Royal Societies of London and Edinburgh, member of 

 the Royal Irish Academy, and of Academies in Stockholm, 

 Upsala, Berlin, Manchester and Philadelphia, and Inspector Gen- 

 eral of his majesty's mines in the Kingdom of Ireland. It is 

 probable, therefore, that he presents a fair idea of the opinions 

 which underlay the Lehmann classification. According to Kir- 

 wan's book the rocks were originally in a soft or liquid state, the 

 center of the earth was supposed to be hollow, or the whole 

 earth was a solid exterior crust with immense empty caverns 

 within. The materials of the earth were then in a state of fusion 

 or solution, and by condensation, as time progressed, the solids 

 were crystallized out and deposited from the chaotic fluid. The 

 water contracted the surface and lowered upon it by sinking into 

 the interior cavities. With the deposition of the primitive rocks 



