124 SCIENTIFIC ILLUSTRATIONS [For 



of variation which it has undergone, as compared with most 

 domestic animals, is singularly small. This fact can be partially 

 accounted for by selection not having come largely into play. 

 Birds of all kinds, which present many distinct races, are valued 

 as pets or ornaments ; no one makes a pet of the goose : the 

 name indeed, in more languages than one, is a term of reproach." 



VA. 



" Footprints on the Sands of Time." 



In our own islands footmarks of Sauroid animals have been 

 detected in the Coalfield south of Edinburgh, and the impres- 

 sions of the feet of another reptilian animal have been found in 

 the Coalfield of the Forest of Dean. The American geologists 

 have evidences, in their lowest Silurian (Potsdam) beds, of 

 numerous trails of animals, probably crustaceans, by which a 

 film of mud or sand formed by one tide was tracked and 

 burrowed before another covered the impressions, and left them 

 to future ages as proofs of layers deposited on the shores of 

 former lands. Some of the coal sandstones in the environs of 

 Manchester exhibit on their surfaces the clearest indications bf 

 having been shore- deposits, certain tracks having been marked 

 on them by animals which must have crawled at ebb tides. 

 Longfellow speaks of " footprints on the sands of time ; " and 

 here they are literally. In a metaphorical sense we may trace 

 also through the centuries the footprints of our intellectual 

 giants. They are seen in our literature, in our picture galleries, 

 in our sculpture, in our architecture, and our laws. SL 



The Mightiness of Silent Forces. 



We often overlook the mightiness of forces because of their 

 silence. Were we endowed by Nature with a microscopic eye, 

 and were the integuments of plants completely transparent, the 

 world of vegetation would not meet us with that aspect of 

 immobility and repose in which it now presents itself to our 

 senses. The interiors of the cellular structures of vegetables 

 are ceaselessly animated by the most diversified currents, rotary, 

 rising and falling, dividing and ramifying, or altering their 

 direction, as is made manifest by the movement of the granular 



