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gradually covered with sand by the rippling waves. That this 

 process took place gradually and slowly in the Solenhofen strata, 

 is evident also from another circumstance, for we frequently find 

 the cavities of insects, the head, thorax, and body filled up with 

 regular crystals of calcareous spar. Hence the pressure of the 

 stratum overlying the insects must have been very slight, when 

 such delicate parts as the abdominal segments of a dragon fly 

 could oppose resistance for a sufficient length of time to admit of 

 the formation of crystals. Naturally there do occur, here and 

 there, in the Solenhofen strata, impressions of insects obtained in 

 a difi'erent way, which admit of the idea of a very heavy pressure 

 from the superincumbent strata ; yet these specimens are scarce, 

 and form only a small proportion of the entire number." Now 

 the state of preservation of fossil insects from English strata of 

 this period is, as Dr. Hagen goes on to observe, in strong 

 contrast to that of the Solenhofen insects. The fossil insects 

 from English strata are seldom entire, and their remains generally 

 consist of single ^vings, or parts of wings. The imperfect con- 

 dition of the English insects may be accounted for by supposing 

 that their deposition did not take jilace gradually and slowly, hke 

 that of the Solenhofen insects, but only after they had for a long 

 time been tossed about by storms or other commotions, or 

 remained for years soddening in Avater. It may seem almost 

 incredible that such fragile things as the wings of insects should 

 have been preserved to us at all, except under extremely favour- 

 able circumstances ; but, according to Dr. Hagen, the wings of 

 insects are almost indestructible in water, and he states that he 

 " has kept the wings of dragon flys in water for years without 

 observing the slightest change in their texture." On the 

 Continent of Europe, so far as present researches enable us to 

 judge, the secondary rocks do not, as a rule, appear to contain 

 fossil insects in any abundance ; but to this rule the Solenhofen 

 slate of Bavaiia, and the Lias of Schambelen in the Swiss Alps, 

 form a striking exception. For our knowledge of the fossil 

 insects of the Solenhofen slate we are indebted chiefly to 



