4 HISTORY OF GEOLOGY AND PALEONTOLOGY. 



Lower Egypt had been at one time covered by the sea, and 

 that the material carried down by the Nile had been discharged 

 into the sea-basin between Thebes and Memphis and the 

 present delta, and gradually filled it up. Herodotus could not 

 form any definite opinion as to the cause of the Nile inunda- 

 tions, although he gave a careful report of the hypotheses then 

 in favour. 



Heraclitus (born 535 B.C.) thought there was in the universe 

 nothing stable, nothing lasting. Everything was in a state of 

 constant change, like a stream in which new waves endlessly 

 supplant the old. For him fire was the primeval force, which 

 unceasingly transformed itself, pervaded every portion of the 

 universe, produced individuals, and again destroyed them. 

 Fire became the ocean, and that again earth, and the breath 

 of life. The rising vapours burned in the air and formed the 

 sun, which was renewed from day to day. Thus Heraclitus 

 taught that although the universe always had been and always 

 would be, no portion of it had ever been quiescent, and that 

 from time to time a new world was constructed out of the 

 old. 



Pythagoras, who was born at Samos about the year 582 B.C., 

 and afterwards went to Crotona in Italy, is one of those 

 eminent leaders of thought around whose name and teaching 

 much that is mythical has gathered. The exponents of his 

 teaching in subsequent ages too often attributed to the early 

 Pythagoreans conceptions which were in reality foreign to the 

 doctrines of the great master himself, and it is extremely 

 difficult to disentangle the threads of original thought from the 

 confused web of tradition. It is clear that the Pythagoreans 

 indulged more in abstract speculation than their predecessors, 

 and gave less attention to observation of nature. They sought 

 to explain natural phenomena chiefly by analogy with definite 

 numerical relationships. An ordered universe depended, 

 according to the Pythagoreans, upon the principle of numbers. 

 Consequently the properties of numbers, individually con- 

 sidered, in sequence, and in combination, were investigated 

 with a zeal which enabled the school to lay the foundation of 

 important mathematical advances. In applying the principle 

 of numbers to musical sound, Pythagoras is reputed to have 

 arrived at a true conception of musical intervals and to have 

 established the theory of the octave. On the other hand, the 

 Pythagoreans were less happy in their application of the limita- 



