No. 2.] MATTHEW — POST-PLIOCENE MOLLUSCA. 105 



•continental glacier of vast thickness and weight, which descended 

 southward across Canada and New England. So far as my own 

 observations go, it seems to me quite impossible to explain all the 

 phenomena of the Drift or Post-Pliocene period in Acadia upon 

 either of these two theories taken alone : both glacier and ice- 

 berg have had free scope and course here, but to describe fully 

 the results of their presence would swell these preliminary 

 remarks to undue proportions. Suffice it to say that the period 

 opened with the operation of that powerful agent — ice — which 

 gave rise to the drift striae, and the boulder-clay ; and that the 

 marine life of the epoch was extremely scanty.* 



The Boulder-clay is universally distributed in Acadia, being 

 found near the tops of the highest hills and throughout the 

 whole extent of the country. It is a deposit which so far as we 

 know is without stratification, and consists of an intimate mix- 

 ture of sand and clay, in which innumerable striated blocks and 

 fragments of stone are imbedded : these stones have been trans- 

 ported southward, and the majority, in the southern part of 

 New Brunswick, m;iy be traced to ledges of old rock not more 

 than ten or fifteen miles north of the places where they are now 

 found. 



Throughout a great part of the country the Boulder-clay is 

 overlaid by another deposit which has been denominated " modi- 

 fied drift" from the fact that the materials of which it is made 

 up are derived from the Boulder-clay and have beeu sorted and 

 rearranged by water. It is well developed in the valley of the 

 St. Lawrence River, where Dr. Dawson divides it into the Leda 

 clay and Saxicava sand. A threefold division of the formation 

 would be more appropriate in xicadia, for in this country the 

 Leda clay is separated from the Boulder-clay by stratified sand 

 .and gravel beds, enclosing smoothed boulders : in its lower part 

 this arenaceous group has irregular beds of Boulder-clay alterna- 

 ting with the sandy strata ; but the mass of it is distinguished 

 from the typical Boulder-clay, by the absence of clay, the round- 

 ness and smoothness of the stones, and the well marked stratifi. 

 cation. No trace of organic remains has yet been found in this 

 group, and the arrangement of the beds in many places is such 

 as to indicate that they were deposited in waters of considerable 



* Dr. Dawson affirms the presence of I'ortlandia glacialis in true 

 " Till" or Boulder Clay on Murray Bay River in the Valley of the 

 St. Lawrence. 



