Page:The Journal of geology (IA journalofgeology11893univ).pdf/406

the terraces of the Connecticut have a much greater southward slope than those on the smaller river, and the depression was not sufficient to reverse the stream. The conditions on the two sides of the trap ridge were not the same.

To sum up, then, the history of the Farmington seems to have been as follows: Its original consequent course was southeast on the crystallines and perhaps across the trap ridge at Cook's Gap, from which course it was turned in the Tertiary cycle by a stream whose course was approximately that of the Mill river of to-day. The damming of the valley by the deposits of the Upper Farmington, and the depression in the north accompanying the ice retreat, reversed the river at Farmington, and it took a new course on the terrace deposits, escaping by the sag in the trap at Tariffville into the Connecticut valley.

The Quinnipiac. The gorge of the Quinnipiac, already mentioned several times, seems closely comparable to the gorge of the Farmington. It is not of the Tertiary cycle, and is best referred to the inter-glacial or post-glacial epochs. We should expect the Quinnipiac, instead of turning eastward, to cut through this sandstone ridge, to continue southward along the Mill river valley. Dana^[1] finds from the heights of the terraces that the drainage of the terrace-building period was not along the Quinnipiac, but along the Mill river, and concludes that the Quinnipiac gorge was obstructed by an ice-dam. I have not as yet studied it enough in detail to do more than express the opinion here reiterated, that this gorge is later than the cycle in which the open sandstone lowland on either side of it was excavated. Its topographic form would put it in the cycle which has been called post-Tertiary.

The Scantic. In the Scantic we have a typical example of a river whose lower course is manifestly of a later date than the upper. In this it is similar to several of our Atlantic rivers, notably those of North Carolina, whose upper courses are on the Piedmont crystallines, being probably established previous to the Cretaceous baselevelling, and whose lower courses stretch