BECEEATIVE SCIENCE. 



29 



SCIENCE ON THE SEA-SHORE. 



I. FLINTS AND SPONGES. 

 



Waem work on the shiuing sands, with tlie 

 blazing sun in the meridian, and the surface 

 of the broad and scarcely-ruffled sea co- 

 vered with a throbbing vapour, that seems 

 too oppressed to rise freely, and panting for 

 a friendly breath of wind to help it in its 

 journey upward. Not a cloud to give a 

 momentary shadow and idea of coolness; 

 and the heat seeming to come down in pulses 

 to which every vein in the body beats time. 

 "Were it not for the faint gurgle of the sea 

 breaking into sluggish lines of foam along 

 the pebbled shore as the tide rises, we shoidd 

 believe we were consigned to an oven, to 

 test the limits of human endurance. But 

 the water is real — it sparkles as it breaks 

 along the shingle, and its music is cool to 

 the ear, and mentally subdues the fever of 

 the body. But to turn one's eyes to the 

 chalk, which right and left seems to be in- 

 candescent, is to risk blindness ; it is too 

 white to be gazed upon intently, and we 

 must wait tUl the fervent sun sinks, hissing, 

 into the wet horizon. There, after all, is a 

 cool nook, and just in the very place in which 

 we may trace the lines of flints as they lie in 

 regular strata from the base to the summit. 



What is flint P How it has puzzled the 

 philosophers to answer the question, and how 

 has the microscope assisted them ! The most 

 interesting point in the first step of the in- 

 quiry is, that flint always occurs in chalk, 

 and usually in separate nodules, as flies occur 

 in amber. There is one notable exception, 

 in the continuous stratum which rises from 

 the beach near St. Margaret's Bay, and there 

 may be a few other examples ; but the rule 

 is, to find flints in beds, pretty regularly 

 sprinkled over the surface, and every block 

 having its own contour, distinctness, and 

 individuality. Why should it occur in chalk ? 



and if a deposit from water, why shoidd it 

 be in separate nodides P 



Take a thin slice of flint, properly pre- 

 pared for the microscope, and let the in- 

 strument unravel its history. If used to 

 the detection of fossil infusoria, you will 

 hardly fail to find them in it, and you 

 gain one step towards an answer as to 

 its history. Organized forms have had 

 something to do with its formation; at 

 some time very far back in the past there 

 has been animal life there, and that life was 

 marine. But you cannot account for the for- 

 mation of separate and independent nodules 

 of silica, scattered over a bed of chalk, by 

 the help of these infusoria. Try a splinter 

 of flint broken off in the rough ; but be very 

 careful not to spoil your object-glass by bring- 

 ing the two surfaces into close contact. Now 

 what do you seeP Eemains of shells, and 

 here and there distinct traces of a sort of 

 reticulated structure, sparry incrustations 

 of a contour which you cannot but believe 

 is derived from some organic form, long 

 since annihilated. These appearances are re- 

 peated in various specimens, and have a 

 general relationship one to the other, especi- 

 ally in the interlacing lines and spiculae of 

 which they consist. Now observe this speci- 

 men of Pachi/matisma Johnstonii, which I 

 have obtained on purpose for the comparison. 

 Do you note the starry spicule with which 

 its pores are beset, and which you see are 

 flinty, and constitute the basis of the crea- 

 ture's skeleton ? There is your index to the 

 history of flints. The organic structure va- 

 riously observable in the specimens owe 

 their origin to sponges, in the structure of 

 which sUex is the main ingredient, just as 

 carbonate of lime is the principal material in 

 the bony skeletons of madrepores. 



If we revert back in imagination to the 

 period when these flints were formed, we 

 see the floor of the ocean abundantly peopled 

 with marine creatures. There were star- 

 fishes, echinites, madrepores, and infusoria ; 



