20 THE CANADIAN NATTTRALI&T. [March 



be'ow the water-level. Again in Sombra, on the banks of the 

 Sydenham river, which is very little above the level of Lake St. 

 Clair, a well ten feet above the river passed through 100 feet 

 of clay before meeting the black shales of the Portage group, 

 while in Maidstone, on the shore of Lake St. Clair, and a very 

 few feet above its level, 109 feet of clay were found overlying the 

 Corniferous limestone. The greatest depth of Lake St. Clair is 

 scarcely thirty feet, and that of the south-western half of Lake 

 Erie does not exceed sixty or seventy feet, so that it would seem 

 that these present lake basins have been excavated from the 

 quaternary clays which, in this region, fill a great ancient basin, 

 hollowed out of the paleozoic rocks, and including in its area the 

 south-western part of the peninsula of Ontario. 



ON THE CHOICE OF A MICROSCOPE. 



By J. Baker Edwards, P.H.D., F.O.S. 



Much excellent advice has been given in English scientitic 

 periodicals on this subject. Meanwhile manufacturers have been 

 improving the instrument in many respects, and probably a larger 

 class now exists who desire assistance in the choice of a Micros- 

 cope than could be found 20 years ago, when the variety of choice 

 was less embarrassing. Since that period, — when the Exhibition 

 of 1851 proved the superiority of our leading English maker.? 

 over their foreig-n competitors — great improvements have been 

 introduced and a large variety of forms have been strongly 

 recommended as possessing peculiar advantages, such as the 

 elegant light tube frame, and magnetic stage of Mr. Ladd, the 

 solid body and elliptical stage of Mr. Pillischer, the useful and 

 cheap instruments of ^Ir. Highley, and the Universal Microscope 

 of Smith & Beck. These varieties are, however, rather curious 

 and ingenious than desirable, and must be left to individual taste 

 to select. I shall not, therefore, dwell upon their peculiar excel- 

 lences, but describe only such general typical forms as may 

 probably be obtained or easily procured in this country; and I 



