'272 Scientific Intelligence. 



In contrast with these two features of erosion, that of the post- 

 Liguanea epoch of submergence has been of small proportions; 

 indeed, the post- Liguanea elevation is so recent that it has not 

 passed beyond the Btage of making narrow deep canons. On 

 account of this formation overlying the remains of the Layton 

 series the different features of erosion, up to an altitude of GOO 

 feet, are geologically preserved, while at greater altitudes they 

 are not so easily distinguishable from those produced before the 

 Liguanea epoch; yet when one has become familiar with the 

 features of erosion, the respective epochs are generally recogniz- 

 able. The post-Liguanea canon-making epoch was characterized 

 by an elevation of 150-200 feet more than at present; for the 

 continuations of the existing rivers are traceable to that depth 

 across the submerged coastal plains. The subsidence which 

 caused the drowning of these valleys reached to an elevation ol 

 10-25 feet below the present level; since which time the coral 

 reefs of the coast have emerged to this amount. 



Numerous as these oscillations appear, all of them, since the 

 post-Layton elevations have been of comparatively small and 

 diminishing proportions. These changes of level of land and sea 

 have occurred on the other West India islands and on the con- 

 tinent ; and from the amount of work accomplished, the Pleisto- 

 cene period seems to have been one of long duration. 



Outside of Jamaica, the geological features of that beautiful 

 island would not be of special interest, except that here we find 

 additional evidence, both upon land and the adjacent sea, support- 

 ing the theory of the high continental conditions of the West 

 Indian region in the early Pleistocene period, when the land 

 stood more than two miles above the present altitude, uniting 

 North and South America, as is set forth in the " Reconstruction 

 of the Antillean Continent." 



2. Resemblance between the Declivities of High Plateaus and 

 those of Submarine Antillean Valleys; by J. W. Spencer. 

 Tranactions of the Canadian Institute, vol. v,pp. 359-3G8, 1898. — 

 This paper is a sequel to the " Reconstruction of the Antillean 

 Continent,"* as in it the analysis of the slopes of the drowned val- 

 leys had not been considered. Both in the land and in the 

 submarine valleys, their gradients are of two kinds: Those of 

 rivers which are flowing over continental plains or upon the 

 surface of high tablelands, where the declivities of the streams 

 are so gentle as to be often reduced to even a foot per mile ; (2) 

 where the valleys are descending from higher to lower plateaus, 

 in which case the descent is over a series of precipitous steps, 

 separated by short gradation planes, marking pauses in the 

 elevation of the land. Thus, if the mean descent of such a valley 

 be taken, an average gradient would be entirely misleading. While 

 the mean slope may reach from 100 to 200 feet per mile, it is 

 found that in reality it is composed of perhaps twenty abrupt 

 steps, with almost level flats between. Or the steps may reach a 



*Bull. Geol. Soc. Am., vol. vii, pp. 103-140. 1894. 



