COAL MEASURES BENEATH ESSEX. 13I 



primaeval crust (a state of things perhaps not altogether unlike that 

 which exists in the larger planet Jupiter), that crust was much 

 thinner than the present lithosphere, or stony outer structure, 

 of the globe. Into this great question we cannot enter here.- 

 Now this thin crust at an early period began to depart from the 

 geometrical regularity of a spherical surface, and as the whole globe 

 contracted from further loss of heat, the crust had to bend and 

 throw itself into a series of slight flexures, rising in parts into broad 

 flat arches or domes (which initiated our present continents in out 

 line) and sinking in other parts into vast saucer-like hollows (out- 

 lining the ocean-basins of the globe). Further contraction neces- 

 sitated other movements of a more local nature, their localities being 

 determined by lines of weakness in the crust as it gradually thickened, 

 though not equally in all parts. Such movements have given 

 direction to most of the mountain-chains of the globe, some of which 

 have since been worn down by denudation to mere stumps, as is the 

 case with the Scottish and Welsh Highlands, the mountains of 

 Bohemia and Central Germany, and others that might be mentioned. 

 Along the early axes of elevation in many cases, further movements 

 (at the early stages feeble) have taken place, as the result of the 

 lateral thrust due to contraction of the globe as a whole, and in 

 their later stages have lifted into the sky such present lofty ranges 

 as the Alpine System, the Pyrenees, the Himalayas, the Andes. 



Two general accompaniments of such axes of elevation must be 

 mentioned — (i) the fundamental crystalline rocks (the gneisses and 

 schists of the text-books) form everywhere the inner cores of these 

 elevated regions ; (2) such disturbances have given rise to innumer- 

 able foldings and faultings of the crust, producing lines and points 

 of weakness, through which enormous quantities of molten material 

 have escaped from the interior, giving us another class of crystalline 

 rocks known to the geologist as eruptive igneous rocks. These have 

 been simply passive accompaniments of elevation ; the notion (found 

 in the older text-books) that they were the active agents of elevation 

 may be relegated to the limbo of geological fiction. This has all 

 been discussed by myself and others elsewhere, but its discussion 

 here would be out of place, and involve scientific technicalities which 



2 It is dealt with in my '•Chemical and Physical Studies in the Metamorphism of Rocks " 

 (Longiiians, 1889). The view there worked, out has since been adopted by a leading American 

 geologist as furnishing the only clue to the observed relations of the Archaean Rocks of the 

 North American Continent and was warmly appreciated at the time by Professor Hermann 

 Credner. of Leipzig, whom I regard as one of the \ery foremost of European geologists. These 

 ideas are slowly working their way into the text-books published in this country. 



