GEOMETRIDJE GEONOMA. 



627 



fire, then, that rocks have been elevated, that strata 

 have been hardened, and that those strata have 

 resulted, which an examination of the earth's surface 

 unfolds. The production of soils, and of alluvial 

 land, is considered as dependent upon causes the 

 same as those referred to in the other theory. 



It will be observed that Hutton refers to fire as 

 well as water for the production of our present rocks ; 

 the former consolidating, hardening-, and elevating ; 

 the latter collecting and depositing the strata. 



We have thus brought together a brief outline of 

 the principal systems, or rather hypotheses, that have 

 been employed to illustrate the history of our earth ; 

 but very considerable light has been thrown on the 

 changes which it has undergone by those geologists 

 who have peculiarly directed their attention to the 

 remains of a former world that are so richly embedded 

 in its surface. This part of the subject has, however, 

 been fully discussed in the article FOSSIL REMAINS, 

 to which we must refer our readers, as well as to the 

 various articles relating to geology as they occur in 

 their alphabetical order. To those who wish for an 

 intimate acquaintance with all the facts bearing on 

 this subject, we would recommend a study of the 

 voluminous but interesting " Transactions of the 

 Geological Society," which, added to the printed 

 labours of Phillips, Conybearc, Ure, Buckland, Boue, 

 Lycil, and Cuvier, contain the most extraordinary 

 collection of facts that has yet been brought together 

 in any branch of natural history. 



GEOMETRIDJ3 (Stephens). A veiy extensive 

 family of lepidopterous, nocturnal, or rather semi- 

 nocturnal, insects, known to collectors by the name of 

 slender-bodied moth, by which term they are well dis- 

 tinguished from the BombycidfE (feathered full bodies) 

 and Nocluidcc (thread-horned full bodies) From the 

 other families of moths, Tortricidae, Tencidce, &c., 

 they are distinguished by their larger size. Mr. 

 Stephens has described more than three hundred 

 British species belonging to this family, divided into 

 upwards of sixty genera. The family is further cha- 

 racterised by the antcnncc of the males being gene- 

 rally feathered, and those of the females simple ; the 

 palpi are mostly short and three-jointed, and the 

 spiral tongue varies considerably in length, some- 

 times, indeed, being obsolete ; the legs are long and 

 slender, the posterior tibiae being furnished with 

 two pairs of spurs, one being placed in the centre, 

 and the other at the extremity ; the wings are of a 

 large size, generally horizontally extended, and much 

 variegated with markings of various colours, whence 

 these insects are amongst the most beautiful of the 

 Lcpidoptera. The name of the family is derived 

 from the Greek words ge, the earth, and meter, to 

 measure, and is given to these insects on account of 

 the peculiar motions of the caterpillars, which are 

 ordinarily termed " loopers" by collectors, and which, 

 when creeping along, somewhat resemble a pair oi 

 compasses alternately opened and shut. An ex- 

 ample of this kind of caterpillar has been figured in 

 the article ABRAXAS. When unemployed in walk- 

 ing, they stretch themselves out in a straight line 

 adhering to the twigs by their hind legs only, and, in 

 many instances, so completely resembling bits o! 

 sticks, as to deceive the beholder. A figure of the 

 caterpillar of the swallow-tail moth (Ouraptyx sambit- 

 ccria) is. given in our article CATERPILLAR. 



Some of these caterpillars also possess the power 

 when alarmed, of throwing themselves from the 



eaves or twigs, having first attached thereto the end 

 >f a silken thread, by means of which they suspend 

 hcmselves in the air ; this thread, which proceeds 

 rom the mouth, is lengthened or shortened at will ; 

 \nd it is by means of this thread that the caterpillar 

 Icscends from the tree to the earth to undergo its 

 chrysalis state ; it also employs the same thread to 

 remount to its original situation when the danger is 

 massed ; this motion being effected by the insect seiz- 

 ng hold of the thread with its intermediate legs, be- 

 .weeri which it accumulates a greater or less mass, 

 n proportion as it advances. Some species form for 

 themselves slight cocoons of silk under ground, others 

 amongst the leaves, and some are naked in the chry- 

 salis state, and are suspended only by the tail. In 

 their perfect state these insects offer but few particulars 

 .vorthy of remark. Unlike the majority of the moths, 

 some of these slender bodies fly during the after- 

 noon. They abound in woods and hedges, and their 

 flight is much lighter than that of the Bombyddce or 

 Noctuida. The males of some species present the 

 curious character of being apparently six-winged, the 

 lower wings being provided with a large flattened 

 oval appendage, somewhat like a miniature wing. 

 These form the genus Loliuphora of Curtis. In se- 

 veral other of the species the females are destitute 

 of wings, as in the Plialccna, brumata, defoliaria, pc~ 

 daria, &c. The first of these species, as the name 

 implies, is found in the winter flying, during the 

 month of December, about the leajjess whitethorn 

 hedges, in search of its mate. In the Regne Animal 

 Latrcille united these insects in a single " sous- 

 genre." Mr. Curtis has, however, divided them into 

 two families, PhalcEnidcc and Geometridce, in which 

 the antenngeof the males are either feathered or merely 

 ciliated, or even simple ; but this step, as Mr. Stephens 

 observes, is " evidently unnatural," since some genera 

 have the male antenna? simple, though closely allied 

 to insects having strongly pectinated antennae, whilst 

 some females have pectinated antennae, although 

 placed with others in which they are simple, and in 

 which some of the males have them scarcely pec- 

 tinated. 



With the exception of the variations of structure 

 and peculiarities of habit above noticed, which, of 

 course, constitute the leading characters of the sec- 

 tional and generic divisions established in this family, 

 it must be evident that in so large an assemblage of 

 objects possessing so many characters in common, 

 the distinguishing marks must be of a comparatively 

 trivial nature ; hence, it will not be necessary for us, 

 in a work of this nature, to indicate the names of 

 the numerous generic divisions introduced into the 

 family, and still less to describe them, and shall, 

 therefore, only notice that the genus Geomelra, as 

 now restricted, comprises a beautiful group of moths, 

 called " thorns," in which the wings are all angu- 

 lated, and the male antennae pectinated ; that one of 

 the most beautiful, although one of the commonest 

 species is the Abraxas grossulariata, figured in our 

 first volume ; that another beautiful species, being 

 the largest of the family, is the swallow-tail moth, 

 above noticed, in which the hind wings are furnished 

 with short tails, and that there is a very extensive 

 and pretty group in the family, known by collectors 

 under the name of the carpet moths, in which the 

 wings are of a white or pale colour, with numerous 

 undulating bands of slate-grey and other colours. 



GEONOMA (Willdenow). A genus of orna- 

 RR2 



