Sir,

Having some idea of the extent to which your time must be occupied, I should not have troubled you with acknowledging the receipt of your very kind and considerate letter,¹ were it not that for some time past I have been longing for an opportunity of consulting you on one or two points connected with Denudation.²

You may, perhaps, have noticed a number of articles by me in the Geological Magazine which have given rise to a rather warm controversy on the origin of escarpments, valleys, and plains.³ With the exception of a little assistance from Mr Hull (of the Ord. Survey) and Mr Kinnahan (Irish Survey) I have been left to fight the battle with the Subaërial school singlehanded.⁴ In endeavouring to answer opponents, I have been gradually led not to place too much reliance on sea-coast action, and after allowing a certain amount of influence to ice, I have been driven to oceanic currents, periodically increased in intensity by sudden upheavals or depressions of the earth’s crust, as the main excavators of valleys.⁵

My object in writing is to take the liberty of asking if you have published any thing, or know of any thing that has been published, on the excavating power of currents, and whether you think that their action on the chalk of the south of England (with or without ice) would be sufficient to explain the hollowing, rounding scoring, escarpmenting, and terracing, which form so striking a feature of the chalk downs.⁶ For upwards of a year I have been wandering among these downs with the view of generalizing all the facts connected with the terracing and scoring of their slopes. When I ventured a short time ago (too inconsiderately) to assert that there were raised beaches among the chalk downs, Mr. Poulett Scrope ridiculed the idea in the Geological Mag., and referred all the terraces to the action of the plough.⁷ I think I can now demonstrate that, however much the terraces may have been either enhanced or defaced by cultivation, there are thousands which are of natural origin. The most puzzling characteristic is their very frequent want of horizontality and parallelism, which at first might suggest the idea of currents rather than sea-coast action. But I have noticed a similar absence of horizontal parallelism among the smaller terraces of the North of Scotland & elsewhere. Would you kindly inform me if this be a characteristic of any of the terraces you have discovered in S. America, and whether unequal upheaval, or irregular formation during oscillations of the land, would offer an explanation.⁸ The finest series I have seen is near Stockbridge, on the side of the Andover and Romsey Railway.⁹ They are parallel, but gently inclined longitudinally. They are covered with fractured flints, mixed with thoroughly rounded pebbles.

I enclose the very rough & imperfect sketch I took on the spot.¹⁰

Hoping you will kindly excuse the liberty I take in asking for a hint or two on these subjects when you happen to have a little leisure, | I am, Sir, | Your very obliged & humble Ser^t., | D. Mackintosh

This will be my address for more than a week to come—afterwards Chichester

P.S. I shall gladly embrace the first opportunity of seeing the work you refer to, and shall call attention to the fact probably in the Geological Magazine.¹¹