FOSSIL INFUSORIA. 315 



mitted without farther preparation to a heat sufficient to 

 remove all the cell-contents and softer parts, leaving the 

 siliceous epiderm in a transparent state." 



In the vicinity of Hull many very interesting varieties 

 of Diatomacece have been found, the beauty of the varied 

 forms of which are such as to delight the microscopist ; 

 and, at the same time, some of them are highly useful, as 

 forming that class of test objects which are best calculated 

 of all others for determining the excellence and powers of 

 object-glasses. It has been shown by Mr. Sollitt that 

 the markings on some of the shells are so fine as to range 

 between the 30,000th and 130,000th of an inch; the 

 Pleurosigma strigilis having the strongest markings, and 

 the Pleurosigma acus the finest. 



Fossil Infusoria. Startling and almost incredible as the 

 assertion may appear to some, it is none the less a fact, 

 established beyond all question by the aid of the micro- 

 scope, that some of our most gigantic mountain-ranges, 

 such as the mighty Andes, towering into space 25,250 feet 

 above the level of the sea, their base occupying so vast an 

 area of land; as also our massive limestone rocks, the 

 sand that covers our boundless deserts, and the soil of 

 many of our wide-extended plains ; are principally com- 

 posed of portions of invisible animalcules. And, as Dr. 

 Buckland truly observes : " The remains of such minute 

 animals have added much more to the mass of materials 

 which compose the exterior crust of the globe than the 

 bones of elephants, hippopotami, and whales." 



The stratum of slate, fourteen feet thick, found at Bilin, 

 in Austria, was the first that was discovered to consist almost 

 entirely of minute flinty shells. A cubic inch does not 

 weigh quite half an ounce ; and in this bulk it is estimated 

 there are not less than forty thousand millions of indi- 

 vidual organic remains ! This slate, as well as the Tripoli, 

 found in Africa, is ground to a powder, and sold for 

 polishing. The similarity of the formation of each is 

 proved by the microscope ; and their properties being the 

 same, in commerce they both pass under the name of 

 Tripoli : one merchant alone in Berlin disposes annually of 

 many hundred tons weight. The thickness of a single shell 

 is about the sixth of a human hair, and its weight the mm-,. 



