HARJ)W1CKE*S SCIENCE-GOSSIP. 



85 



supporting heads formed of plates mosaicked to- 

 gether, and terminating in a living network of fingers 

 or meshes, are among the most familiar fossils of the 



upper Silurian limestone 'rocks. Not less wonderful 

 as showing the degree of differentiation which had 

 already gone on, and as illustrating, how, when a 



^. 'MC 





:^■i>■■sv■v^■( 



t\ 



&m\;lSi«l.M^i.-iv>m3SLKi^»..-i'i kiJA Il*^i^,.-Ss>iiij^^«£> 



Fig. 54. Section across Snowdon Rang-e. n, Cambrian grey and purple grits and slates, much dislocated and supporting: 

 Lingula flags, b, Liiigula flags faulted, c. Slates (Llandeilo), dark grey, traversed by eruptive dykes,* (the bedding almost 

 obliterated) followed by d, bluish-grey and brownish sandstone and slate (Lower Caradoc beds), with felspathic ashes and 

 volcanic grit, d* e, Upper part of the Caradoc (or Bala) beds, fossiliferous, with calcareous and felspathic ashes. 





^-=n,-v 



Fig. 55. 1, Marsupio-crinites rnelatns : 3, Maunided base of the arms; 



3, Proboscis of the same inserte'l in the sliell of Acnicuhu Italmtis ; 



4, Reduced figure of Crotalo-criinis rugosus : tbebai^-like cluster of 

 arms surmounting the small round pelvis ; s, the latter, of natural 

 size, with the stomach-plates stripped off, and sbowiiig the base of 

 the many-lingered arms ; 6, the flat stomachal surface, showing also 

 the branching of the arms from their bases; 7, a part of the reti- 

 culated congeries of fingers, each joint being anch) losed to its neigh- 

 bour on eitlier side. 



mechanical or physiological contrivance 

 has reached a certain stage, the idea 

 becomes stereotyped — are the fossil star- 

 fishes from the same beds. We have seen 

 specimens as perfectly preserved, and 

 with all the ambulacral perforations as 

 distinct, as in recent species. The fol- 

 lowing group (fig. 56) give a good illus- 

 tration of the manner with which the 

 " Geological Record " has done its work 

 in preserving the organisms of some 

 of the most ancient seas of the globe. 



We finished the last pages of the book 

 with regret, but still with the determi- 

 nation, by-and-by, to turn them over 

 again. We cordially reconimeud it as a 

 book likely not only to profit the stu- 

 dent and pedestrian, but stay-at-home 

 people, who like to know what is to be 

 seen in the world without their going 

 to see it. 



MICROSCOPY. 



•^^^>,^^^ 



Fig. 56. Fossil Star-fish from Lower L ull )w Rocks; 1, 2, 

 Protastcr Miltoni, a form of Ophiuridcie with numerous 

 plates; 2 a, small portion of a Protastcr magnified; 3. 

 Palseocoma Marstoni ; 4. P, Colvini. These are star-flshes 

 allied to Palraipes and Pteraster. 



Dark Lines in Field of View. — 1 

 feel it a duty to reply to your corre- 

 spondent " G. W." (in Science-Gossip for last 

 month, page 63), relating to the question why 

 the higher powers do not work so satisfactorily 

 witli the binocular arrangement as the lower 

 ones do. The fact is, that an inch is about the 

 highest power that can be well used with the 

 usual arrangement; that is to say, the prism 

 fixed at the bottom of the eye-tubes. But when we 

 wish to use higher object-glasses, as i, \, &c., we 

 must cither have our object-glasses made very much 

 shorter, so as to bring their lenses much nearer to 

 the prism, or, what is still better, have a small 

 prism fixed in the tube of the object-glass itself. 1 

 have an sth thus made, which performs admirably, 

 showing a perfect field ; but the prism is not more 

 than about the «th of an inch in size, and fixed 

 closely to the back lenses of the " objective ; " being 



