O THE LAKE OF STENNI8. 



eye, and still more unequivocally by the irregular complexity 

 of fabric which it exhibits under the microscope, — by its 

 speck-like life-points or canaliculi, that remind one of air- 

 bubbles in ice, — its branching channels, like minute veins, 

 through which the blood must once have flown, — and its 

 general groundwork of irregular lines of coi-puscular fibre, 

 that wind through the whole, like currents in a river studded 

 with islands, — ^it was as truly osseous in its composition as 

 the solid bones of any of the reptiles of the Secondary or the 

 quadrupeds of the Tertiary periods. And in form it closely 

 resembled a large roofing-nail. With this bone our more 

 practised palseontologists are but little acquainted, for no re- 

 mains of the animal to which it belonged have yet been dis- 

 covered in Britain to the south of the Grampians, nor, except 

 in the Old Ked Sandstone of Russia, has it been detected 

 anywhere on the Continent. Nor am I aware that, save 

 in the accompanying woodcut (fig. 1), it has ever been 

 figured. The amateur geologists of Caithness and Orkney 

 have, however, learned to recognise it as the "petrified nail." 

 The length of the entire specimen in this instance was five 

 seven-eighth inches, the transverse breadth of the head two 

 inches and a quarter, and the thickness of the stem nearly 

 three-tenth parts of an inch. This nail-like bone formed a 

 characteristic portion of the Asterolepis, — so far as is yet 

 known, the most gigantic ganoid of the Old Red Sandstone. 

 There were various considerations which led me to regard 



o 



the " petrified nail" in this case as one of the most interest- 

 ing fossils I had ever seen ; and, before quitting Orkney, to 

 pursue my explorations farther to the south, I brought two 

 intelligent geologists of the district,* to mark its place and 

 character, that they might be able to point it out to geolo- 

 gical visitors iu the future, or, if they preferred removing it 



* Dr George Garson, Stromness, and Mr William Watt, jun., SkaiU. 



