THE POPULAR SCIENCE MONTHLY. 



ocean-shore, so as to reveal its existence. 

 The surface covering of the ice was the sur- 

 face of the country, and, over many miles 

 north from its actual termination, it sup- 

 ported a varied and even rank vegetation." 

 Professor Winchell observes that the facts 

 reported by Mr. Dall throw light on the 

 mamier of formation and deposit of the till, 

 and on the origin of Jcames. The kames 

 are gravel-ridges lying in till-covcred coun- 

 tries, occupying the lower situations and 

 generally bordered on either side by a paral- 

 lel strip of swamp or low land. Now, if we 

 suppose that the till before its deposit lay on 

 the surface of the ice, it is plain that the 

 surface drainage, gathering into streams, 

 would produce deep channels in the ice- 

 sheet, in the bottom of which would be 

 gathered such stones and gravels as the 

 stream could not carry away, and these 

 would gradually sink deeper into the ice, 

 perhaps to the rocky floor itself. When 

 the ice had entirely disappeared, the bed of 

 coarser matters thus formed "would lie 

 undisturbed in its beautiful stratification, 

 where the river produced it " ; while on ei- 

 ther side would be first the swampy or low 

 land produced by the wash of the stream, 

 and outside of this the unmodified till. 



UndtTgrowth and Forest - Trees. M. 



Gourmand has recently described some ob- 

 servations which he has made on the influ- 

 ence of thickets upon the decomposition of 

 vegetable matter and the growth of large 

 trees. A thicket may be formed in the 

 course of eight or ten years after the under- 

 growth has started ; as it rises in height we 

 can at last distinguish between the atmos- 

 phere beneath it and the superior atmos- 

 phere to which the tops of the larger trees 

 are exposed. Seventeen years of watching 

 and periodical measuring of the growth of 

 the trees of a tract bearing a deciduous un- 

 dergrowth and a larger coniferous growth 

 have shown that the rate of growth of the 

 larger trees diminishes as the undergrowth 

 becomes more dense ; the only exceptions arc 

 in glades where the undergrowth sends up 

 vertical limbs instead of spreading out side- 

 wise. The rate of growth thus appears to 

 be modified according as the light is or is 

 not able to penetrate the depth of the wood, 

 and, as carbonic acid is in a corresponding 



degree more or less rapidly formed from 

 the decomposition of the substances com- 

 posing the humus. M. Gourmand concludes 

 from these observations that light, when it 

 reaches the gi'ound after passing through 

 foliage, stimulates the production of carbonic 

 acid in decompositions that engender hu- 

 mus in proportion as that gas is decom- 

 posed by the green parts ; that the growth 

 of the larger trees is retarded, although 

 their green parts stand out in full air and 

 light, where the lower thicket cuts the light 

 off too much from the soil and diminishes 

 its reflex action on their tops ; that this ef- 

 fect is governed largely by the arrangement 

 of the limbs of the undergrowth, as it is 

 less marked in glades, where they take a 

 vertical direction ; and that the humus un- 

 der too dense an undergrowth loses a part 

 of its efficiency, and presents an analogy 

 with barn-yard manure, which will remain 

 inert for several years if it is buried too 

 deeply. 



The Weather, and Summer Diarrhoeas. 



Mr. G. B. Longstaff has recently pointed 

 out, in an address before the Society of Medi- 

 cal Officers of Ilealth, some facts concerning 

 the prevalence of summer diarrhoea in Eng- 

 land, which are not fully accounted for by 

 the prevailing theories of its origin. lie 

 distinguishes between two kinds of diar- 

 rhoea: one general, prevailing throughout 

 the year, affecting persons at all ages, and 

 nearly evenly distributed in town and coun- 

 try; and a specific form, which prevails in 

 the summer months and affects most per- 

 sons at the extremes of life, particularly in- 

 fants of less than two years old, and which 

 is not definitely modified by changes of 

 season. The second form is, as a rule, a 

 disease of towns, but different towns are 

 differently affected by it. The summer of 

 1880 was a warm one in England, with the 

 mean temperature in August and September 

 above the average, and a high rainfall in 

 July and September, while little rain fell in 

 August; the death-rate from diarrhoea in 

 England and Wales exceeded the average of 

 the previous ten years by nearly fifty per 

 cent. The comparison of the mortality 

 from this cause in different towns, as be- 

 tween the towns and with the general mor- 

 tality of the kingdom, failed to establish 



