因迟复来信致歉because of answering one’s letter late

dear david:

i am afraid that you will think me unpardonably negligent in not having answered your letter dated 7, december sooner, but when i have told you the reason, i trust you will be convinced that the neglect was excusable. when your letter arrived, i was just in hong kong. as my family could not forward it to me during my absence, it has been, therefore, lying on my desk until the moment when i took it up. now the first thing i have to hasten to do is to write to you these few lines to express my deep regret. 

i enjoyed many pleasant sights during my trip. i shall be pleased to give you an account to of them when i see you next. 

sincerely yours, 

tom